Distributed administration of access to information

ABSTRACT

A scalable access filter that is used together with others like it in a virtual private network to control access by users at clients in the network to information resources provided by servers in the network. Each access filter use a local copy of an access control data base to determine whether an access request made by a user. Changes made by administrators in the local copies are propagated to all of the other local copies. Each user belongs to one or more user groups and each information resource belongs to one or more information sets. Access is permitted or denied according to of access policies which define access in terms of the user groups and information sets. The rights of administrators are similarly determined by administrative policies. Access is further permitted only if the trust levels of a mode of identification of the user and of the path in the network by which the access is made are sufficient for the sensitivity level of the information resource. If necessary, the access filter automatically encrypts the request with an encryption method whose trust level is sufficient. The first access filter in the path performs the access check and encrypts and authenticates the request; the other access filters in the path do not repeat the access check.

CROSS REFERENCE TO RELATED PATENT APPLICATIONS

The present patent application claims priority from the provisionalapplications No. 60/093,542, Schneider, et al., Distributed NetworkSecurity, filed Mar. 10, 1997, and No. 60/040,262, Schneider, et al.,Secure Electronic Network Delivery, also filed Mar. 10, 1997. Thepresent patent application is further one of four patent applicationsthat have the same Detailed Description and assignee as the presentpatent application and are being filed on the same date. The fourapplications are:

U.S. Ser. No. 09/034,507, David Schneider, et al., Distributedadministration of access to information;

U.S. Ser. No. 09/034,503, David Schneider, et al., User interface foraccessing information, now abandoned;

U.S. Ser. No. 09/034,576, David Schneider, et al., Secure delivery ofinformation in a network, issued Jan. 23, 2001 as U.S. Pat. No.6,178,505; and

U.S. Ser. No. 09/034,587, David Schneider, et al., Scalable accessfilter, issued Aug. 15, 2000 as U.S. Pat. No. 6,105,027, DavidSchneider, et al., Techniques for eliminating redundant access checkingby access filters.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates generally to control of access to data and relatesmore specifically to control of access to data in a distributedenvironment.

2. Description of Related Art

The Internet has revolutionized data communications. It has done so byproviding protocols and addressing schemes which make it possible forany computer system anywhere in the world to exchange information withany other computer system anywhere in the world, regardless of thecomputer system's physical hardware, the kind of physical network it isconnected to, or the kinds of physical networks that are used to sendthe information from the one computer system to the other computersystem. All that is required for the two computer systems to exchangeinformation is that each computer system have an Internet address andthe software necessary for the protocols and that there be a routebetween the two machines by way of some combination of the many physicalnetworks that may be used to carry messages constructed according to theprotocols.

The very ease with which computer systems may exchange information viathe Internet has, however, caused problems. On the one hand, it has madeaccessing information easier and cheaper than it ever was before; on theother hand, it has made it much harder to protect information. TheInternet has made it harder to protect information in two ways:

It is harder to restrict access. If information may be accessed at allvia the Internet, it is potentially accessible to anyone with access tothe Internet. Once there is Internet access to information, blockingskilled intruders becomes a difficult technical problem.

It is harder to maintain security en route through the Internet. TheInternet is implemented as a packet switching network. It is impossibleto predict what route a message will take through the network. It isfurther impossible to ensure the security of all of the switches, or toensure that the portions of the message, including those which specifyits source or destination, have not been read or altered en route.

FIG. 1 shows techniques presently used to increase security in networksthat are accessible via the Internet. FIG. 1 shows network 101, which ismade up of two separate internal networks 103(A) and 103(B) that areconnected by Internet 111. Networks 103(A) and 103(B) are not generallyaccessible, but are part of the Internet in the sense that computersystems in these networks have Internet addresses and employ Internetprotocols to exchange information. Two such computer systems appear inFIG. 1 as requestor 105 in network 103(A) and server 113 in network103(b). Requestor 105 is requesting access to data which can be providedby server 113. Attached to server 113 is a mass storage device 115 thatcontains data 117 which is being requested by requestor 105. Of course,for other data, server 113 may be the requester and requestor 105 theserver. Moreover, access is to be understood in the present context asany operation which can read or change data stored on server 113 orwhich can change the state of server 113. In making the request,requester 105 is using one of the standard TCP/IP protocols. As usedhere, a protocol is a description of a set of messages that can be usedto exchange information between computer systems. The actual messagesthat are sent between computer systems that are communicating accordingto a protocol are collectively termed a session. During the session,Requestor 105 sends messages according to the protocol to server 113'sInternet address and server 113 sends messages according to the protocolto requestor 105's Internet address. Both the request and response willtravel between internal network 103(A) and 103(B) by Internet 111. Ifserver 113 permits requester 105 to access the data, some of themessages flowing from server 113 to requestor 105 in the session willinclude the requested data 117. The software components of server 113which respond to the messages as required by the protocol are termed aservice.

If the owner of internal networks 103(A and B) wants to be sure thatonly users of computer systems connected directly to networks 103(A andB) can access data 117 and that the contents of the request and responseare not known outside those networks, the owner must solve two problems:making sure that server 113 does not respond to requests from computersystems other than those connected to the internal networks and makingsure that people with access to Internet 111 cannot access or modify therequest and response while they are in transit through Internet 111. Twotechniques which make it possible to achieve these goals are firewallsand tunneling using encryption.

Conceptually, a firewall is a barrier between an internal network andthe rest of Internet 111. Firewalls appear at 109(A) and (B). Firewall109(A) protects internal network 103(A) and firewall 109(B) protectsinternal network 103(B). Firewalls are implemented by means of a gatewayrunning in a computer system that is installed at the point where aninternal network is connected to the Internet. Included in the gatewayis an access filter. a set of software and hardware components in thecomputer system which checks all requests from outside the internalnetwork for information stored inside the internal network and onlysends a request on into the internal network if it is from a sourcesthat has the right to access the information. Otherwise, it discards therequest. Two such access filters, access filter 107(A), and accessfilter 107(B), appear in FIG. 1.

A source has the right to access the requested information if twoquestions can be answered affirmatively:

Is the source in fact who or what it claims to be?

Does the source have the right to access the data?

The process of finding the answer to the first question is termedauthentication. A user authenticates himself or herself to the firewallby providing information to the firewall that identifies the user. Amongsuch information is the following:

information provided by an authentication token (sometimes called asmartcard) in the possession of the user;

the operating system identification for the user's machine; and

the IP address and the Internet domain name of the user's machine.

The information that the firewall uses for authentication can either bein band, that is, it is part of the protocol, or it can be out of band,that is, it is provided by a separate protocol.

As is clear from the above list of identification information, thedegree to which a firewall can trust identification information toauthenticate a user depends on the kind of identification information.For example, the IP address in a packet can be changed by anyone who canintercept the packet; consequently, the firewall can put little trust init and authentication by means of the IP address is said to have a verylow trust level. On the other hand, when the identification informationcomes from a token, the firewall can give the identification a muchhigher trust level, since the token would fail to identify the user onlyif it had come into someone else's possession. For a discussion onauthentication generally, see S. Bellovin and W. Cheswick, Firewalls andInternet Security, Addison Wesley, Reading, Mass., 1994.

In modem access filters, access is checked at two levels, the Internetpacket, or IP level, and the application level. Beginning with the IPlevel, the messages used in Internet protocols are carried in packetscalled datagrams. Each such packet has a header which containsinformation indicating the source and destination of the packet. Thesource and destination are each expressed in terms of IP address andport number. A port number is a number from 1 to 65535 used toindividuate multiple streams of traffic within a computer. Services forwell-known Internet protocols (such as HTTP or FTP) are assigned wellknown port numbers that they ‘listen’ to. The access filter has a set ofrules which indicate which destinations may receive IP packets fromwhich sources, and if the source and destination specified in the headerdo not conform to these rules, the packet is discarded. For example, therules may allow or disallow all access from one computer to another, orlimit access to a particular service (specified by the port number)based on the source of the IP packet. There is, however, no informationin the header of the IP packet about the individual piece of informationbeing accessed and the only information about the user is the sourceinformation. Access checking that involves either authentication of theuser beyond what is possible using the source information or determiningwhether the user has access to an individual piece of information thuscannot by done at the IP level, but must instead be done at the protocollevel.

Access checking at the application level is usually done in the firewallby proxies. A proxy is a software component of the access filter. Theproxy is so called because it serves as the protocol's stand-in in theaccess filter for the purposes of carrying out user authenticationand/or access checking on the piece of information that the user hasrequested. For example, a frequently-used TCP/IP protocol is thehyper-text transfer protocol, or HTTP, which is used to transferWorld-Wide Web pages from one computer to another such computer system.If access control for individual pages is needed, the contents of theprotocol must be inspected to determine which particular Web page isrequested. For a detailed discussion of firewalls, see the Bellovin andCheswick reference supra.

While properly-done access filtering can prevent unauthorized access viaInternet 111 to data stored in an internal network, it cannot preventunauthorized access to data that is in transit through Internet 111.That is prevented by means of tunneling using encryption. This kind oftunneling works as follows: when access filter 107(A) receives an IPpacket from a computer system in internal network 103(A) which has adestination address in internal network 103(B), it encrypts the IPpacket, including its header, and adds a new header which specifies theIP address of access filter 107(A) as the source address for the packetand the IP address of access filter 107(B) as the destination address.The new header may also contain authentication information whichidentifies access filter 107(A) as the source of the encrypted packetand information from which access filter 107(B) can determine whetherthe encrypted packet has been tampered with.

Because the original IP packet has been encrypted, neither the headernor the contents of the original IP packet can be read while it ispassing through Internet 111, nor can the header or data of the originalIP packet be modified without detection. When access filter 107(B)receives the IP packet, it uses any identification information todetermine whether the packet is really from access filter 107(A). If itis, it removes the header added by access filter 107(A) to the packet,determines whether the packet was tampered with and if it was not,decrypts the packet and performs IP-level access checking on theoriginal header. If the header passes, access filter 107(B) forwards thepacket to the IP address in the internal network specified in theoriginal header or to a proxy for protocol level access control. Theoriginal IP packet is said to tunnel through Internet 111. In FIG. 1,one such tunnel 112 is shown between access filter 107(A) and 107(B). Anadditional advantage of tunneling is that it hides the structure of theinternal networks from those who have access to them only from Internet111, since the only unencrypted IP addresses are those of the accessfilters.

The owner of internal networks 103(A) and 103(B) can also use tunnelingtogether with Internet 111 to make the two internal networks 103(A andB) into a single virtual private network (VPN) 119. By means of tunnel112, computer systems in network 103(A) and 103(B) can communicate witheach other securely and refer to other computers as if network 103(A)and 103(B) were connected by a private physical link instead of byInternet 111. Indeed, virtual private network 119 may be extended toinclude any user who has access to Internet 111 and can do thefollowing:

encrypt Internet packets addressed to a computer system in an internalnetwork 103 in a fashion which permits an access filter 107 to decryptthem;

add a header to the encrypted packet which is addressed to filter 107;and

authenticate him or herself to access filter 107.

For example, an employee who has a portable computer that is connectedto Internet 111 and has the necessary encryption and authenticationcapabilities can use the virtual private network to securely retrievedata from a computer system in one of the internal networks.

Once internal networks begin using Internet addressing and Internetprotocols and are connected into virtual private networks, the browsersthat have been developed for the Internet can be used as well in theinternal networks 103, and from the point of view of the user, there isno difference between accessing data in Internet 111 and accessing it ininternal network 103. Internal network 103 has thus become an intranet,that is, an internal network that has the same user interface asInternet 111. Of course, once all of the internal networks belonging toan entity have been combined into a single virtual private intranet, theaccess control issues characteristic of the Internet arise again—exceptthis time with regard to internal access to data. While firewalls at thepoints where the internal networks are connected to Internet 111 areperfectly sufficient to keep outsiders from accessing data in theinternal networks, they cannot keep insiders from accessing that data.For example, it may be just as important to a company to protect itspersonnel data from its employees as to protect it from outsiders. Atthe same time, the company may want to make its World Wide Web site on acomputer system in one of the internal networks 103 easily accessible toanyone who has access to Internet 111.

One solution to the security problems posed by virtual private intranetsis to use firewalls to subdivide the internal networks, as well as toprotect the internal networks from unauthorized access via the Internet.Present-day access filters 107 are designed for protecting the perimeterof an internal network from unauthorized access, and there is typicallyonly one access filter 107 per Internet connection. If access filtersare to be used within the internal networks, there will be many more ofthem, and virtual private networks that use multiple present-day accessfilters 107 are not easily scalable, that is, in virtual privatenetworks with small numbers of access filters, the access filters arenot a serious burden; in networks with large numbers of access filters,they are. Among the problems posed by present-day access filters whenthey are present in large numbers in a virtual private network are thefollowing:

Present-day access filters are designed to be centrally-administered bya small number of data security experts. As the number of access filtersincreases, central administration becomes too slow, too expensive, andtoo error-prone.

Present-day access filters are designed on the assumption that there areonly a small number of access filters between the source and destinationfor data. Where there are many, the increase in access time and thereduction in access speed caused by the filters becomes important.

Present-day access filters are designed on the assumption that theInternet side of the filter is completely insecure and the internalnetwork side of the filter is completely secure. In fact, both kinds ofnetworks offer varying degrees of security. Because security addsoverhead, the access filter should neither require nor provide more thanis necessary.

Present-day access filters, where they use encryption, require that eachaccess filter know encryption keys for each other access filter. Largenumbers of access filters require substantial duplicated effort in keymaintenance.

Present-day access filters do not provide any mechanism for giving theuser a view of the information resources that corresponds to the user'saccess rights.

What is needed if intranets and virtual private networks are to achievetheir full promise is access filters that do not present the aboveproblems for scalability.

SUMMARY OF THE INVENTION

The aspect of making access filters scalable which is addressed by theclaims attached hereto is decentralized administration of accessfilters. The decentralized administration is done using two classes ofpolicy:

access policy, which determine how users may access information. Theusers belong to sets of users called user groups and the informationbelongs to sets of resources called information sets and access policyis defined in terms of access by user groups to information sets; and

administrative policy, which determines how administrators mayadminister and delegate access policies and the subjects and objects ofaccess policies. Administrative policy is defined in terms of sets ofadministrative users and objects.

A member of an administrative user set which administers an object maymake administrative policy for the object; this permits anadministrative user set to delegate its right to administer the objectto another administrative user group. The access policy is administeredby means of policy maker policy, which is how administrative user groupsmay make access policy. The policy maker policy is defined in terms ofadministrative user groups and sets of resources.

When the access filter is set up, a built-in administrative policy givesa built-in administrative user group called the security officer theright to make administrative policy for all objects in the system.Members of the security officer user group delegate rights to makeadministrative policy to other administrative user groups as requiredfor the VPN in which the access filter is installed. Generally, thepolicy maker policy is set up to give only a small number of high-levelsecurity experts the right to make access policy. The remainingadministrative policy is delegated to user groups who have the requisiteknowledge of the entities being administered. For example, if a usergroup corresponds to a department in a business, administration of thedepartmental user group may be delegated to the departmental secretary.

The entities in the virtual private network to which the access filterbelongs are hierarchically organized. In general, entities at a lowerlevel of the hierarchy inherit policies which apply at higher levels.Thus, the access policies which apply to a user group also apply to itssubsets and an administrator who has administrative access to the usergroup also has administrative access to its subsets.

Delegation is done by changing the administrative policy. To delegateadministration of the user group to the departmental secretary, theadministrator for the administrative user group that administers thedepartmental user group adds the departmental secretary to theadministrative user group. If that administrative user group administersother user groups as well and it is desired to give the departmentalsecretary administrative authority only over the departmental usergroup, the administrator for the administrative user group makes a newadministrative user group that contains only the departmental secretaryand the administrator who defines administrative policy for thedepartmental user group adds an administrative policy which permits thenew administrative user group containing the departmental secretary toadminister the departmental user group. The departmental secretary cannow add members to and delete members from the departmental user group.Because of inheritance, anyone who belongs to an administrative usergroup which can administer a user group which is above the departmentaluser group in the hierarchy can also administer the departmental usergroup.

Among the objects to which administrative policies apply are usergroups, information sets, and available resources, that is, theservices, servers, access filters, and network structure making up thevirtual private network. The administrator of an object also controlsattributes of the object such as the sensitivity level of resources andthe trust level of modes of user identification, network links, andencryption methods.

The access policy and the administrative policy are defined in accesscontrol information. Each access filter has a local copy of the accesscontrol information. An administrative user may edit the local copy andchanges are propagated to the other access filters in the virtualprivate network. One of the access filters has a master copy, andchanges are first propagated to the master copy and the changed mastercopy is then propagated to all of the other access filters.

Administration of the access policy and of the entities is done by meansof graphical user interfaces. The graphical user interface foradministering an access policy has a three-part display; in one part,the user groups are displayed; in a second part, the information sets towhich the user groups are to be given data access are displayed; in athird part, the policies are displayed. In creating a new policy, a usergroup is selected in the first part, an information set is selected inthe second part, and a policy is defined. The new policy then appears inthe third part. An evaluator in the graphical user interface permits theuser to see how current policies affect access by user groups toinformation sets. The graphical user interface for administering anobject has a list of entities that the user using the interface canadminister and a set of administrative operations. Other objects andadvantages of the invention will be apparent to those skilled in thearts to which the invention pertains upon perusing the followingDetailed Description and Drawing, wherein:

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is an overview of techniques used to control access ofinformation via the Internet;

FIG. 2 is an overview of a VPN that uses access filters incorporatingthe techniques disclosed herein;

FIG. 3 is an overview of an access control database that is used in theaccess filters;

FIG. 4 shows access checking and tunneling in a VPN that uses accessfilters incorporating the techniques disclosed herein;

FIG. 5 shows access by a “roamer” to information in the VPN;

FIG. 6 is a table used in defining the relationship between sensitivityand trust levels and authentication and encryption techniques;

FIG. 7 is an example of the application of SEND;

FIG. 8 is a flow chart of the policy creation process;

FIG. 9 shows a display used to define user groups;

FIG. 10 shows a display used to define information sets;

FIG. 11 shows a display used to define access policies;

FIG. 12 shows a display used to define an access filter 203;

FIGS. 13A and B are a schema of the part of access control database 301that defines user groups;

FIG. 14 is a schema of the part of access control database 301 thatdefines information sets;

FIG. 15 is a schema of the part of access control database 301 thatdefines sites in the VPN and the servers, services, and resources ateach site;

FIGS. 16A and B are a schema of the part of access control database 301that defines policies;

FIGS. 17A, B and C are a schema of the part of access control database301 that defines servers;

FIG. 18 shows the display used in the IntraMap interface;

FIG. 19 shows how changes are made to access control database 301;

FIG. 20 is a detailed block diagram of the architecture of an accessfilter 203;

FIG. 21 is a diagram of the structure of an MMF file 2303;

FIG. 22 is a diagram of a message sent using SKIP;

FIGS. 23A, B, and C are a table of the MMF files employed in a preferredembodiment;

FIG. 24 is a diagram of an implementation of the IntraMap interface; and

FIG. 25 is a diagram illustrating delegation in VPN 201.

The reference numbers in the drawings have at least three digits. Thetwo rightmost digits are reference numbers within a figure; the digitsto the left of those digits are the number of the figure in which theitem identified by the reference number first appears. For example, anitem with reference number 203 first appears in FIG. 2.

DETAILED DESCRIPTION

The following Detailed Description will first provide an overview ofaccess filters that are easily scalable, of how they are used to controlaccess in intranets, and of how they can be used to construct virtualprivate networks. Thereupon, the Detailed Description will providedetails of the access control database used in the filters, of themanner in which it is changed and those changes are distributed amongthe filters, and of the manner in which an individual filter controlsaccess.

A Network with Access Filters that Do Not Interfere with Scalability:FIG. 2

FIG. 2 shows a virtual private network (VPN) 201 in which access to datais controlled by access filters that are designed to avoid the problemsposed by multiple access filters. VPN 201 is made up of four internalnetworks 103 which are connected to each other by Internet 121. Alsoconnected to VPN 201 via Internet 121 is a roamer 217, that is, acomputer system which is being used by a person who may access data inintranet 201, but is connected to the internal networks only by Internet121. Each internal network 103 has a number of computer systems orterminals 209 belonging to users and a number of servers 211 whichcontain data that may be accessed by users at systems or terminals 209or by a user at roamer 217. However, no computer system or terminal 209or roamer 217 is connected directly to a server 211; instead, each isconnected via an access filter 203, so that all references made by auser at a user system to a data item on a server go through at least oneaccess filter 203. Thus, user system 209(i) is connected to network213(i), which is connected to access filter 203(a), while server 211(i)is connected to network 215(i), which is also connected to access filter203(a), and any attempt by a user at user system 209(i) to access dataon server 211(i) goes through access filter 203(a), where it is rejectedif the user does not have the right to access the data.

If VPN 201 is of any size at all, there will be a substantial number ofaccess filters 203, and consequently, scaling problems will immediatelyarise. Access filters 203 avoid these problems because they are designedaccording to the following principles:

Distributed access control database. Each access filter 203 has its owncopy of the access control database used to control access to data inVPN 201. Changes made in one copy of the database are propagated to allother copies.

Distributed administration. Any number of administrators may bedelegated responsibility for subsets of the system. All administratorsmay perform their tasks simultaneously.

Distributed access control. Access control functions are performed atthe near-end access filter 203. That is, the first access filter 203 inthe path between a client and the server determines if the access isallowed and subsequent access filters in the path do not repeat theaccess checks made by the first access filter.

End-to-end encryption. Encryption occurs between the near-end accessfilter and the furthest encryption endpoint possible. This endpoint iseither the information server itself or the far-end access filter203—the one last in the route from client to server. Dynamic tunnels arecreated based on current network routing conditions

Adaptive encryption and authentication. Variable levels of encryptionand authentication requirements are applied to traffic passed throughthe VPN, based on the sensitivity of the information being transmitted.

All of these aspects of the design will be discussed in more detailbelow.

It should be pointed out at this point that access filter 203 may beimplemented in any fashion which ensures that all references to data inVPN 201 which are made by users who may not be authorized to access thatdata go through an access filter 203. In a preferred embodiment, accessfilter 203 is implemented on a server and runs under the Windows NT®operating system manufactured by Microsoft Corporation. In otherembodiments, access filter 203 may be implemented as a component of anoperating system and/or may be implemented in a router in VPN 201.

Distributed Policy Database: FIG. 3

Each access filter 203 has a copy of an access control database 301 thatholds all data relevant to access control in VPN 201. One access filter,shown as access filter 203(a) in FIG. 2, has a master copy 205 of accesscontrol database 301. Because of this, access filter 203(a) is termedthe Master Policy Manager. The master copy 205 is the one that is usedto initialize new access filters 203 or replace a damaged access controldatabase 301. The backup for the master policy manager computer isaccess filter 203(b). Backup 207 is a mirror image of master copy 205.Report manager 209, finally, includes software for generating reportsfrom the information in access control database 301 and from logsobtained from all other access filters 203. Any copy of access controldatabase 301 may be altered by any user who has the access required todo so; as will be described in more detail later, any such alteration ispropagated first to master policy manager 205 and then to all of theother access filters 203 in virtual private network 201.

FIG. 3 is a conceptual overview of access control database 301. Theprimary function of the database is to respond to an access request 309from access filter 203 which identifies a user and an informationresource with an indication 311 of whether the request will be grantedor denied. The request will be granted if both of the following aretrue:

The user belongs to a user group which data base 301 indicates mayaccess an information set to which the information resource belongs; and

the request has a trust level which is at least as high as a sensitivitylevel belonging to the information resource.

Each user belongs to one or more of the user groups and each informationresource belongs to one or more information sets; if none of the usergroups that the user belongs to is denied access to an information setthat the resource belongs to and any of the user groups that the userbelongs to is allowed access to any of the information sets that theinformation resource belongs to, the user may access the informationresource, provided that the request has the requisite trust level.

The sensitivity level of a resource is simply a value that indicates thetrust level required to access the resource. In general, the greater theneed to protect the information resource, the higher its sensitivitylevel. The trust level of a request has a number of components:

the trust level of the identification technique used to identify theuser; for example, identification of a user by a token has a highertrust level than identification of the user by IP address.

the trust level of the path taken by the access request through thenetwork; for example, a path that includes the Internet has a lowertrust level than one that includes only internal networks.

if the access request is encrypted, the trust level of the encryptiontechnique used; the stronger the encryption technique, the higher thetrust level.

The trust level of the identification technique and the trust level ofthe path are each considered separately. The trust level of the pathmay, however, be affected by the trust level of the encryption techniqueused to encrypt the access request. If the request is encrypted with anencryption technique whose trust level is higher that the trust level ofa portion of the path, the trust level of the portion is increased tothe trust level of the encryption technique. Thus, if the trust level ofa portion of a path is less than required for the sensitivity level ofthe resource, the problem can be solved by encrypting the access requestwith an encryption technique that has the necessary trust level.

The information contained in database 301 may be divided into five broadcategories:

user identification information 313, which identifies the user;

user groups 315, which defines the groups the users belong to;

information resources 320, which defines the individual informationitems subject to protection and specifies where to find them;

information sets 321, which defines groups of information resources;

trust information 323, which specifies the sensitivity levels ofinformation resources and the trust levels of user identifications andnetwork paths; and

policy information 303, which defines access rights in terms of usergroups and objects in VPN 201.

Policy information is further divided into access policy 307,administrative policy 305, and policy maker policy 306.

access policy 307 defines rights of access by user groups to informationsets;

administrative policy 305 defines rights of user groups todefine/delete/ modify objects in VPN 201. Among the objects are accesspolicies, information sets, user groups, locations in VPN 201, servers,and services; and

policy maker policy 306 defines rights of user groups to make accesspolicy for information sets.

The user groups specified in the administrative policy and policy makerpolicy portions of database 301 are user groups of administrators. InVPN 201, administrative authority is delegated by defining groups ofadministrators and the objects over which they have control in database301. Of course, a given user may be a member of both ordinary usergroups 317 and administrative user groups 319.

Identification of Users

User groups identify their members with user identification information313. The identification information identifies its users by means of aset of extensible identification techniques. Presently, theseidentification techniques include X.509 certificates, Windows NT Domainidentification, authentication tokens, and IP address/domain name. Thekind of identification technique used to identify a user determines thetrust level of the identification. Where strong identification of a useror other entity that an access filter 203 communicates with is required,VPN 201 employs the Simple Key Management for Internet Protocols (SKIP)software protocol, developed by Sun Microsystems, Inc. The protocolmanages public key exchange, authentication of keys, and encryption ofsessions. It does session encryption by means of a transport keygenerated from the public and private keys of the parties who areexchanging data. Public keys are included in X.509 certificates that areexchanged between SKIP parties using a separate protocol known as theCertificate Discovery Protocol (CDP). A message that is encrypted usingSKIP includes in addition to the encrypted message an encryptedtransport key for the message and identifiers for the certificates forthe source and destination of the data. The recipient of the messageuses the identifiers for the certificate of the source of the message tolocate the public key for the source, and uses its keys and the source'spublic key to decrypt the transport key and uses the transport key todecrypt the message. A SKIP message is self-authenticating in the sensethat it contains an authentication header which includes a cryptographicdigest of the packet contents and modification of any kind will renderthe digest incorrect. For details on SKIP, see Ashar Aziz and MartinPatterson, Simple Key-Management for Internet Protocols (SKIP), whichcould be found on Feb. 28, 1998 at http://www.skip.org/inet-95.html. Fordetails on X.509 certification, see the description that could be foundon Sep. 2, 1997 at http://www.rnbo.com/PROD/rmadillo/p/pdoc2.htm.

In VPN 201, SKIP is also used by access filters 203 to identifythemselves to other access filters 203 in the VPN and to encrypt TCP/IPsessions where that is required. Access filters 203 can also use thecertificates for the SKIP keys to identify users when they areperforming access checks. Such an identification is particularlytrustworthy and has a correspondingly high trust level. One use for suchidentification by mean of certificate is for trustworthy identificationof a “roamer” 217. The X.509 certificates can be used for useridentification because they relate the key information to informationabout the user.

Access filter 203 uses the following fields of information from thecertificates:

Expiration Date. The date after which the certificate is invalid.

Public Key. The public half of a public-private key pair, as used in theSKIP-based cryptography that Conclave uses.

Certificate Authority Signature. The distinguished name associated withthe authority that issued the certificate.

Serial Number for the certificate

Subject name, the name of the entity the certificate was issued to.

The subject name includes the following subfields (the value inparentheses is the common abbreviation for the field):

Common Name (CN). The given name of the subject, for example, John Q.Public.

Country (C). The country in which the subject resides. Country codes are2-letter codes specified in the X.509 specification.

Locality (L). The location at which the subject resides. This is usuallythe city in which the subject resides, but can be used for anylocation-related value.

Organization (O). The organization to which the subject belongs. This isusually the organization's name.

Organizational Unit (OU). The organizational unit for the subject. Thisis usually the department for the subject, for example, “sales”. TheX.509 certificate allows up to four of these fields to exist.

A Certificate Authority used with access filters 203 issues certificateswith all of these fields. Further, the four OU fields can be used todefine additional categories. The information used to describe a user ina certificate is available to the administrators of data base 301 foruse when defining user groups. If the information in the certificatesproperly reflects the organizational structure of the enterprise, acertificate will not only identify the user, but show where the userfits in the enterprise's organization and to the extent that the usergroups in data base 301 reflect the organizational structure, the usergroups that the user belongs to.

As will be explained in more detail later, one way in which members ofuser groups may be defined is by certificate matching criteria whichdefine the values of the fields which a certificate that belongs to amember of a given user group must have. The certificate matchingcriteria can be based on as few or as many of the above fields asdesired. For example, the certificate matching criteria for theEngineering user group might be the organization field and anorganization unit field specifying the engineering department. Otherinformation that identifies a user may be used to define members of usergroups as well.

Information Sets

Information sets hold collections of individual information resources. Aresource may be as small as an individual WWW page or newsgroup, butmost often it will consist of a Web directory tree and its contents, FTPaccounts, or major Usenet news categories. Two information sets, 219(j)and (k), are shown in one of the servers of FIG. 2. While it iscompletely up to the administrators of access control database 301 todetermine what information is included in an information set, theinformation in a given set will generally be information that is relatedboth topically and by intended audience. Example information sets for acorporation might be HR policies, HR Personnel Records, and PublicInformation.

Access Policy 307

Conceptually, access policy 307 consists of simple statements of theform:

Engineers allowed access to engineering data Internet allowed access topublic web site

The first column specifies user groups; the last column specifiesinformation sets. The middle column is the access policy—allow or deny.

Database 301 permits hierarchical definition of both user groups andinformation sets. For example, the Engineers user group may be definedas including a Hardware Engineers user group, a Software Engineers usergroup, and a Sales Engineers user group. Similarly, the engineering datainformation set may be defined as including a hardware engineering datainformation set, a software engineering data information set, and asales engineering data information set. Access rights are inheritedwithin hierarchies of user groups. Thus, a user who belongs to theHardware Engineers user group also automatically belongs to theEngineers user group for access checking purposes. Access rights aresimilarly inherited within hierarchies of information sets. Aninformation resource that belongs to the hardware engineeringinformation set also automatically belongs to the engineering datainformation set for access checking purposes. Thus, if there is anaccess policy that gives Engineers access to engineering data, any userwho is a member of one of the three user groups making up Engineers mayaccess any information resource that belongs to any of the threeinformation sets making up engineering data. The use of inheritance inthe definitions of user groups and information sets greatly reduces thenumber of access policies 307 that are required in access controldatabase 301. For instance, in the above example, a single access policygives all engineers access to all engineering data. Inheritance alsomakes it possible to define virtually all access policies in terms ofallowing access. Continuing with the above example, if there is a usergroup Salespeople that does not belong to Engineers and there is anaccess policy that gives that user group access to sales engineeringdata, a user who is a member of Salespeople will be able to access salesengineering data, but not software engineering data or hardwareengineering data.

A user may of course belong to more than one user group and aninformation resource may belong to more than one information set. Theremay also be different access policies for the various user groups theuser belongs to and the various information sets the informationresource belongs to. When faced with multiple access policies that applyto the user and to the information resource that the user is seeking toaccess, access filter 203 applies the policies in a restrictive, ratherthan permissive way:

If multiple policies allow or deny a user group's access to aninformation set, policies that deny access prevail.

If a particular user is a member of multiple user groups, and multiplepolicies allow or deny access to the information set, policies that denyaccess prevail.

What user groups a user belongs to may vary according to the mode ofidentification used to identify the user. Thus, if no access policiesapply for the user groups that the user belongs to according to themodes of identification that the user has thus far provided to accessfilter 203, access filter 203 may try to obtain additionalidentification information and determine whether the additionalidentification information places the user in a user group for whichthere is a policy regarding the resource. Access filter 203 may obtainthe additional identification information if:

The user has installed the User Identification Client (software thatruns on the user's machine and provides identification information aboutthe user to access filter 203).

The UIC is currently running on the user's machine.

The user has enabled his UIC to pop-up for further authentication. (Theuser has a check box that enables this feature.)

If all of these requirements are true, then access filter 203 will forcethe user's UIC to pop-up and ask for further identification information.Any identification information that the user supplies is saved. Aftereach new piece of user identification information, access filter 203performs the same evaluation process, popping up the UIC window untilidentification information is obtained that places the user in a usergroup for which there is an access policy that permits or denies accessor until the user gives up on his or her request.

Administrative policies 305

The administrative policies 305 implement administration of objects inVPN 201's access control system. Included in the objects are usergroups, information sets, access policies, and what are termed hereinavailable resources, that is, the services, servers, access filters, andnetwork hardware making up VPN 201. An object is administered by one ormore administrative user groups. A member of an administrative usergroup that administers a given object may modify the object and itsrelationship to other objects and may make administrative policy for theobject. As will be explained in more detail later, the fact that amember of an administrative user group that administers an object maymake administrative policy for the object makes it possible for themember to delegate administration of the object. For example, a memberof an administrative user group that administers a Hardware Engineersuser group may make an administrative policy that gives administrationof the Hardware Engineers to a Hardware Engineering Administrator usergroup, thereby delegating administration of Hardware Engineers toHardware Engineering Administrator. It should be noted that the right toadminister an information set is separate from the right to make accesspolicy for the information set. The fact that a user group has the rightto make access policy concerning an information set does not give theuser group the right to make administrative policy for the informationset, and vice-versa. When an access filter 203 is first set up, a singlebuilt-in security officer user group has administrative authority overall of the objects in VPN 201 and over policy maker policy 306.

Inheritance with Administrative Policy

Inheritance works with administrative policy the same way that it doeswith access policy. The user groups, information sets, and availableresources to which administrative policies are directed arehierarchically organized: Within the user groups, user groups that aresubsets of a given user group are at the next level down in thehierarchy of user groups from the given user group. The same is the casewith information sets. Inheritance applies within the hierarchy in thesame fashion as with access policy. Thus, within the user grouphierarchy an administrative user who controls a user group also controlsall subsidiary, contained user groups. Similarly, with the informationset hierarchy an administrative user who controls the information setalso controls all subsidiary, contained information sets and anadministrative user who controls access policy for an information setalso controls access policy for all contained information sets.

There is further a natural hierarchy of available resources. Forexample, one level of the hierarchy is locations. Within a givenlocation, the servers at that location form the next level down, andwithin a server, the services offered by the service form the nextlevel. The administrative user group that has control of any level ofthe available resources tree also controls all lower levels. Forexample, the administrator(s) to whom an administrative policy givescontrol of an access filter 203 has administrative rights to all serversbeneath that site, all services running on those servers and allresources supported by those services.

Delegation: FIG. 25

Delegation is easy in VPN 201 because the members of the administrativeuser group that administers an object may both modify the object andmake administrative policy for it. For example, if an administrativeuser group administers an information set, it can divide the informationset into two subsets and make new administrative policies which giveeach of two other user groups administrative authority over one of thetwo subsets.

FIG. 25 gives an extended example of delegation. In FIG. 25, user groupsand other objects are represented by circles; policy maker policy isrepresented by a square box; policy relationships are expressed bydifferent kinds of arrows: a solid arrow for administrative policy, adotted arrow for policy maker policy, and a dashed arrow for accesspolicy. The part of the figure labeled 2501 shows the situation whenaccess filter 203 is being set up: the built-in Security Officer usergroup 2503 has administrative authority over all of the built-in objects2505 and over policy maker policy 2507. Members of Security Officer usergroup 2503 use their administrative authority to make subsets of objects2505, rearrange the object hierarchies, and set up policy maker policy2507.

One result of the activity of Security Officer user group 2503'sactivity is seen in the section of FIG. 25 labeled 2508. A member ofSecurity Officer user group 2503 has set up an EngineeringAdministrators administrative user group 2509, an Engineers user group2511, and an Engineering Data information set 2513 and has givenEngineering Administrators administrative authority over Engineers andEngineering Data. The member of Security Officer has also set up policymaker policy 2507 so that Engineering Administrators has the right tomake access policy for Engineering Data, as shown by dotted arrow 2510.A member of Engineering Administrators has used that right to makeaccess policy that permits members of Engineers 2511 to accessinformation in Engineering Data 2513, as shown by dashed arrow 2512. Themember of security Officer has thus delegated the administrativeauthority over Engineers 2511, Engineering Data 2513, and over access toEngineering Data to Engineering Administrators 2509.

Security Officer 2503 of course still has administrative authority overEngineering Administrators and can use that authority for furtherdelegation. An example is shown at 2517. A member of Security Officer2503 has divided Engineering Administrators into two subsets:Engineering Personnel Administrators (EPA) 2519 and Engineering DataAdministrators (EDA) 2521. The members of these subsets inheritadministrative rights over Engineers 2511 and Engineering Data 2513 fromEngineering Administrators 2509. The members of EPA 2519 and EDA 2521use these administrative rights to delegate administrative authorityover Engineers 2511 to Engineering Personnel Administrators 2519 andadministrative authority over Engineering Data 2513 to Engineering DataAdministrators 2521. The members of EPA 2519 and EDA 2521 have furtherused their right to make access policy for Engineering Data 2513 tochange the access policy so that access policy for Engineering Data ismade by Engineering Data Administrators 2513, as shown by dotted arrow2523, instead of by Engineering Administrators, thereby delegating thatfunction to Engineering Data Administrators.

Members of Engineering Personnel Administrators and Engineering DataAdministrators can now use their administrative rights over Engineers,Engineering Data, and access policy for Engineering Data to refineaccess to Engineering Data. For example, a member of EngineeringPersonnel Administrators might subdivide Engineers into SoftwareEngineers and Hardware Engineers and a member of Engineering DataAdministrators might subdivide Engineering Data into HardwareEngineering Data and Software Engineering Data. That done, a member ofEngineering Data Administrators might replace the access policy givingEngineers access to Engineering Data with access policies that giveSoftware Engineers access to Software Engineering Data and HardwareEngineers access to Hardware Engineering Data.

In summary, it may be said that the administrators who have control overa user group are responsible for correctly defining membership in theuser group; they may delegate any part of this responsibility to otheradministrators. Similarly, administrators who have control over aninformation set are responsible for correctly including informationresources into the information set; they may delegate any part of thisresponsibility to other administrators. The latter administrators mustof course also be administrators for some available resource from whichthe information being added to the information set may be obtained.Administrators of available resources carry responsibility for overallnetwork and security operation. Likewise, they may delegate theirresponsibilities. Policy maker administrators, finally, hold theultimate control over access to information. They alone may createaccess policies related to specific information sets. In a sense, thepolicy makers determine the overall information sharing policy for theenterprise. Administrators for the user groups, information sets, andavailable resources then determine the particulars of implementation.

Access Control Using Filters 203 and Database 301: FIG. 4

As shown in FIG. 2, an access filter 203 has a position in VPN 201 whichputs it between the client from which the user is requesting access tothe information resource and the server upon which the informationresource resides. The access filter 203 is thus able to control accessby the user to the resource by interceding in the communication betweena user and a service on the server which is able to provide the userwith access to the information resource. In order for the user to gainaccess to the information resource, a session must be establishedbetween the user and the service. In the present context, the termsession is defined liberally, to include well-behaved connectionlessprotocols. When an access filter 203 observes an attempt by a user toinitiate a session with a service, it determines whether access shouldbe permitted. It does so from the known identity of the user, theinformation resource to which the information is being accessed, thesensitivity level of the information, and the trust levels of the useridentification, of the path between the user and the service, and of anyencryption technique used.

FIG. 4 shows how a session can involve more than one access filter 203.Session 402 shown in FIG. 4 involves five access filters 203, numbered403(1..5) in the Figure. Access filters 203 are designed such that thedecision whether to grant a user access to an information resource needonly be made in one of the access filters 203. The key to this featureof access filters 203 is their ability to authenticate themselves toeach other. SKIP is used to do this. Every access filter 203 has anX.509 certificate that binds the access filter 203's keys to the accessfilter's name and is signed by the Certificate Authority for the VPN.Each access filter 203 has the names and IP addresses of all of theother access filters in VPN 201 in data base 301, and upon arrival of asession that is encrypted using SKIP, each access filter uses theSubject Name from the certificates as described above in the discussionof SKIP to determine whether SKIP-encrypted network traffic is fromanother access filter 203 in VPN 201.

If the access filter receiving the session is not the destination of thesession, (that is, the access filter functions simply as an IP routeralong the path), the access filter merely verifies from data base 301that the destination IP address is the IP address of some other accessfilter 203 in VPN 201. If that is the case, then the session is allowedto pass without additional checking. When the request reaches the lastaccess filter 203, the last access filter 203 uses SKIP to decrypt therequest, to confirm that the request was indeed checked by the firstaccess filter 203, and to confirm that the request has not been modifiedin transit.

Thus, in FIG. 4, access filter 403(1) uses its own copy of accesscontrol database 301 to determine whether the user who originates asession has access to the information resource specified for thesession. If access filter 403(1) so determines, it authenticates thesession's outgoing messages and encrypts them as required to achieve theproper trust level. Access filters 403(2..5) then permit the session toproceed because the session is from access filter 403(1) and has beenencrypted with SKIP and neither decrypt the messages nor check themusing their own copies of access control database 301. Access filter403(5) then decrypts the messages, confirms that they were encrypted andtherefore checked by access filter 403(1), and if the messages areintact, forwards them to server 407 that contains the desired resource.Messages in the session which pass between server 407 and user system401 are treated in the same way, with access filter 403(5) encryptingthem if necessary, access filters 403(2..4) passing them through on thebasis of the authentication by 403(5), and access filter 403(1) passingthe message on to system 401 on the basis of the authentication anddecrypting the message if necessary.

What this technique effectively does is to make a tunnel 405 for thesession between access filter 403(1) and access filter 403(5), andbecause of the tunnel, only the access filter 403 closest to the clientneeds to do decryption, access checking, and reencryption. Moreover, thetunnel is equally secure in the internal networks and in Internet 121.In a large VPN, access filter 403(1) is in the best position to checkaccess, because it has access to the most detailed information about theuser who originates the session. The technique of performing the accesscheck at the first access filter 401 further distributes the accesscontrol responsibility evenly across the VPN, allowing it to scale toany size.

End-to-End Encryption: FIG. 5

Tunnel 405 of FIG. 4 extends only from access filter 403(1) to accessfilter 403(5); the messages of the session are unencrypted betweensystem 401 employed by the user and access filter 403(1) and againbetween access filter 403(5) and server 407 that contains theinformation resource. In the case of extremely sensitive information,authentication and encryption may be needed from the near end accessfilter to the end of the path through the network, namely between system403(1) and server 407.

FIG. 5 shows how this is accomplished using access filters 203. Withinthe VPN, authentication and encryption may be used with any clientsystem 401 or 503 or any server system 407 in addition to access filters203. When a client computer utilizes encryption, it uses SKIP toauthenticate the session and encrypt it using a shared secret that isshared between the client computer and a selected access filter 203 andthen sends the encrypted message to the selected access filter 203,thereby effectively establishing a tunnel between the client and theselected access filter 203 and making the selected access filter 203 thefirst access filter 203 for purposes of access checking. At the firstaccess filter 203, the messages are decrypted and access checking isdone. Since SKIP makes available the user's certificate along with theencrypted message, the user's authenticated identity can be used foraccess checking. If the access is permitted, the message is once againencrypted and sent to access filter 403(5) nearest server 407, whichdecrypts it. If data base 301 contains a SKIP name and encryptionalgorithms for server 407, access filter 403(5) retrieves thecertificate for server 407 if necessary and uses SKIP to reencrypt thesession as required for server 407. Otherwise, access filter 403(5)simply sends the message to server 407 in the clear. If the message wasreencrypted for server 407, server 407, finally, receives the encryptedmessage and decrypts it. The access filters 203 intermediate to thefirst access filter 203 and last access filter 203 simply note that themessage is from another access filter and is encrypted with SKIP andpass the message on, as described above. When server 407 retrieves theinformation resource, it either sends it in the clear to access filter403(5) or encrypts the message containing the resource with the key foraccess filter 403(5). The process of decrypting and encrypting describedabove is then performed in reverse, pairwise, from server 407 to accessfilter 403(5), from access filter 403(5) to access filter 403(1), andfinally from access filter 403(1) to the original client system, whichdecrypts it.

The effect of this technique is to construct a tunnel on the pathbetween the client and the server which runs from the access filter 203on the path which is nearest to the client to the access filter 203 onthe path which is nearest to the server. If the client is capable ofencryption and decryption, the tunnel can be extended from the accessfilter nearest the client to the client and if the server is capable ofencryption and decryption, the tunnel can be similarly extended to fromthe access filter nearest the server to the server. Once the firstaccess filter 203 in the path has been reached and has authenticated thesession, no further encryption or decryption is required until theaccess filter 203 nearest the server has been reached. Moreover, accesscontrol database 301 in each access filter 203 contains all of thenecessary identification and certification information for the client,the server, and the access filters 203 in the route. An advantage of theend-to-end encryption technique just described is that it distributesencryption load throughout the network, rather than concentrating it atthe access filters connecting the VPN to the Internet, and therebyenhances scalability.

FIG. 5 shows how the technique works with a session 501 that originateswith a roamer, that is, a client 503 whose connection to the VPN is viaInternet 121. Roamer 503 is equipped with SKIP, as is target server 407on an internal network. When SKIP was configured in the roamer, it wasgiven the certificate for access filter 403(3) and access filter 403(3)was given the certificate for the roamer. When roamer 503 sends amessage belonging to the session, it addresses the message to server 407and encrypts it using a transport key which it shares with access filter403(3). The message is thus tunneled via tunnel 505 to access filter403(3). There, access filter 403(3) decrypts the session, performs theaccess check, and reencrypts it using a transport key for access filter403(5). The subsequent access filters 403 in the path allow the sessionthrough because it is authenticated by access filter 403(3), thusproviding tunnel 507 to at least access filter 403(5). If target server407 is SKIP-equipped, access filter 403(5) extends the tunnel to targetserver 407, as described above.

Adaptive Encryption and Authentication Based on Data Sensitivity: FIGS.6 and 7

An important task in access control in a VPN is determining the minimumamount of security needed by a session. This is important first becauseat least that minimum must be guaranteed and second because moresecurity than is necessary wastes resources. The techniques employed inaccess filters 203 to determine the minimum amount are collectivelytermed SEND (Secure Encrypted Network Delivery). In SEND, access controldatabase 301 contains a data sensitivity level for each informationresource. The data sensitivity level indicates the level of secrecyassociated with the information resource and is assigned to theinformation resource by the security administrator responsible for theresource. An exemplary set of levels is Top Secret, Secret, Private, andPublic.

The levels used to indicate data sensitivity are also used to indicatethe trust level required for the access request. As previouslydescribed, access will be permitted only if the trust level determinedfrom the trust level of the technique used to identify the user, thetrust level of the path of the access request through VPN 201 or thetrust level of any encryption technique used to encrypt messages sentover the path is at least as great as the data sensitivity level for theinformation. The trust levels for user identifications, paths, andencryption algorithms are contained in access control database 301. Withregard to trust levels of paths, the VPN is divided into networkcomponents, each network component being a connected set of IP networksthat is separated from other components by access filters 203. Eachnetwork component has a name and a trust level. For example, an Internetcomponent will have the Public trust level, while an internal networkcomponent may have the Private trust level. The trust level of a givencomponent may be based on its physical security or on the use ofencryption hardware in the component. As each access filter 203 is addedto a VPN, a description of its connections to the components of the VPNis added to database 301. Included in this description are the trustlevels of the networks. Consequently, any access filter 203 can use itscopy of database 301 to determine the trust level of each component ofthe path by which a session will be carried between a client and aserver.

The trust level for a user is determined from the manner in which theaccess request identifies the user. In access control database 301, eachgroup of users has one or more identification techniques associated withit, and each identification technique has a minimum trust level. Thebasic techniques are:

Certificate via SKIP. A user is identified by the name in his or herX.509 certificate used with the SKIP protocol to authenticate andencrypt traffic.

Certificate via User Identification Client. A user is identified by thename in his or her X.509 certificate transmitted to attached accessfilters 203 via a special Conclave client module called the UserIdentification Client. This transmittal is done securely, using achallenge/response mechanism.

Windows Domain ID via User Identification Client. A user who logs in toa Microsoft Windows Domain and has installed the User IdentificationClient automatically has his or her Windows identity, including groupmemberships, transmitted to attached access filters 203. The logon tothe network is done securely within the mechanisms of the NetBIOSprotocol.

Authentication Tokens. Authentication tokens (such as those manufacturedby Security Dynamics Inc. and Axent Corp.) may be utilized in two ways:via the User Identification Client in an out-of-band manner, or in-bandwithin the Telnet and FTP protocols.

IP Address and/or Domain Name. The IP address or fully qualified domainname of the user's computer.

In a preferred implementation of SEND, the identification techniqueshave a predetermined order from most secure to least secure. Thetechniques just listed would be ordered are as they are in the abovelist, with the most secure techniques being at the top of the list. Theordering of the identification techniques is somewhat subjective, butreflects the general security of the identification technique and therigor applied to the distribution and validation of user identities. Anadministrator in VPN 201 then relates the ordered trust levels to theordered identification techniques. For example, if the administratorrelates the private trust level to identification by means ofauthentication tokens, a user who desires to access a resource with theprivate sensitivity level must identify himself or herself by means ofan authentication token or another identification technique which isabove the authentication in the order of identification techniques. Theadministrator of the access filter likewise orders the cryptographicalgorithms available in the VPN from most secure to least secure andrelates the ordered trust levels to the ordered cryptographic algorithmsand orders the network paths employed in VPN 201 and relates the orderedtrust levels to the ordered network paths. These relationships betweentrust levels and orderings with regard to security are included inaccess control database 301. Then a SEND table is constructed whichrelates trust and sensitivity levels to identification and encryptiontechniques. FIG. 6 is a conceptual representation of such a SEND table.

SEND table 601 has three columns: one, 603 for the trust/sensitivitylevels, one, 605, for minimum encryption methods, and one, 607, forminimum identification methods. For details on the encryption methods ofcolumn 605, see Bruce Schneier, Applied Cryptography, John Wiley & Sons,New York, 1994. Each row 609 of the table associates a trust/sensitivitylevel with a minimum encryption level for the path connecting the accessfilter, client, and server and a minimum identification level for theuser. Thus, row 609(1) associates the “top secret” trust/sensitivitylevel with the 3DES encryption algorithm and a user certificate obtainedvia SKIP. A user who wishes to gain access to a resource with thesensitivity level “top secret” must consequently have an identificationthat is certified by SKIP and if the path does not have a “top secret”trust level, the session must be encrypted with the 3DES algorithm. Onthe other hand, as shown by row 609(4), a user who wishes to gain accessto a resource with the sensitivity level “public” may be identified byany method and there is no requirement that the session be encrypted.

When a new session is initiated, the first access filter 203 in the pathemployed for the session proceeds as follows:

1. The access filter determines the information resource being accessedand looks up its sensitivity level in database 301.

2. The minimum authentication for that sensitivity level from SEND table601 specifies which identification mechanisms may be used by the accessfilter to identify and authenticate the user making the access.

3. The first access filter 203 then consults database 301 to determinefrom the user groups the user belongs to and the information sets theresource belongs to whether the user may access the resource.

a. The first step is to determine from the access data base which of theidentification methods used to identify the user have trust levels highenough for the sensitivity level of the resource.

b. Then first access filter 203 consults database 301 using the user'sidentification according to each of the identification methods that hasa high enough trust level to determine the user groups that the userbelongs to.

c. First access filter 203 also consults data base 301 to determinewhich information sets the resource belongs to.

d. Having determined the relevant user groups and information sets,first access filter 203 consults data base 301 to locate the accesspolicies that determine whether access is to be allowed or denied to thesession. If at least one policy allowing access is found and nonedenying access are found, the user is allowed access; otherwise, accessis denied. Details of steps b, c, and d will be given below.

4. If access was not denied, the first access filter 203 then consultsdatabase 301 to determine the network components that make up the routethrough the VPN from the client to the server that contains theinformation resource. The route is considered as having up to threelogical segments:

a. Segment (a), from the client to the first access filter 203. Thissegment may or may not have been encrypted, depending upon whether theclient uses SKIP.

b. Segment (b), from the first access filter 203 to the access filter203 in the path nearest the server; and

c. Segment (c), from the access filter 203 nearest the server to theserver; this segment also may or may not be encrypted.

If segment (a) and segment (c) exist, each will consist of a singlenetwork component. Segment (a) will not exist if the client is on thefirst access filter; segment (c) will not exist if the server is on theaccess filter nearest the server. If segment (b) exists, it will consistof one or more network components. Segment (b) will not exist if thereis only one access filter between the client and server.

5. For each of the segments:

a. For segment (a), any encryption must be done by the client. If thetrust level of segment(a) is not at least as strong as the sensitivityof he resource, or if the trust level of the encryption done by theclient is not at least as strong as the sensitivity of the resource,access is denied.

b. For segment (b), if the weakest trust level of any network componentin the path is greater than or equal to the data sensitivity of theresource, then the traffic is sent without encryption. This correspondsto the case where the network is inherently secure enough to transmitthe data. In the example table above, information resources with aPublic data sensitivity level may be transmitted on any network, asshown by row 609(4). However, the access filters 203 will use SKIP toauthenticate the session, allowing subsequent access filters to pass thesession through without incurring the larger overheads of decryption,access checking, and reencryption. If the weakest trust level for thepath is less than the data sensitivity of the resource, then the SENDtable is consulted for the minimum encryption algorithm required for thesensitivity level and the session is encrypted using that algorithm. Theencryption upgrades the security of the link, making it suitable tocarry data of that given sensitivity and permitting access by the userto the resource.

c. For segment (c), the portion of the path from the access filter 203nearest the server to the server, first access filter 203 determines thetrust levels of segment (c) and of any encryption used in segment (c)from information in database 301. If the trust level of this segment ofthe path is less than the sensitivity level of the information resource,and in that case, if the encryption used in segment(c) is not at leastas strong as that required as the minimum level in the SEND tableconsidering the sensitivity level of the resource, then first accessfilter 203 will deny access.

The above method of determining sensitivity and trust levels ensuresthat access filters 203 employ encryption only as necessary to achievethe necessary trust levels. This reduces the number of sessions thatwill be encrypted while keeping the description of network configurationin database 301 simple and manageable. The result is better scalabilitywith regard to both management of and performance in the VPN.

FIG. 7 provides an example of how the sensitivity level of aninformation resource, the trust level of the user identification, andthe trust level associated with the path between the client and theserver affect access by the user to the information resource. In FIG. 7,a SKIP-equipped user at client 703 initiates a session 701 to obtain aninformation resource 723 which is stored at SKIP-equipped server 705.Segment (a) of the above discussion appears in FIG. 7 at 707; segment(b) appears at 709(1..4); Segment (c) appears at 711. Informationresource 723 has a sensitivity level of “secret”. The first accessfilter 203 that the session encounters is filter 203(1). Access filter203(1) uses its copy of the access control database to determine thesensitivity level of resource 723. Here, the user has used a SKIPcertificate and an examination of SEND table 601 in data base 301 showsaccess filter 203(1) that this kind of user identification meets therequirements for information resources having the “secret” sensitivitylevel, so segment (a) 707 has the required trust level. Consequently,the first access filter goes on to determine the trust level of segments(b) 709(1..4) and (c) between access filter 203(1) and server 705 in theVPN. Segment 709 has subsegments 709(1), 709(2), 709(3), 709(4), and709(5), and first access filter 203(1) checks the trust level of each ofth subsegments in database 301. Segment 709(2) is Internet 121, so itstrust level is “public”, which is the minimum in segment 709. Thenaccess filter 203(1) uses access control data base 301 to check thetrust level of segment 711. It is “secret”. Thus, only segment (b) 709has a trust level that is too low for the path of a session that isaccessing a “secret” information resource 703. To deal with thisproblem, access filter 103(1) must encrypt the session to bring it up tothe necessary trust level. First access filter 203(1) consults SENDtable 601 to determine what kind of encryption is required, and row609(2) indicates that DES encryption is sufficient. First access filter203(1) accordingly encrypts the session using that algorithm and sendsit to access filter 203(5).

In FIG. 7, segment 707 connecting client 703 to access filter 203(1) hasa trust level which is high enough for the resource's sensitivity level,and there is thus no need for client 703 to encrypt its request. Whenthat is not the case, access filter 203(1) will give client 703 accessonly if client 703 has encrypted the request using an encryption methodwhose trust level is sufficient for the sensitivity level of theresource. It is for this reason that roamer 503 in FIG. 5 must beSKIP-equipped. Since roamer 503 accesses access filter 403(3) viaInternet 121, roamer 503's requests can never have more than the publictrust level unless they are encrypted, and in order to have full accessto the resources in VPN 201, roamer 503 must use an encryption methodsuch as the one provided by SKIP whose trust level is sufficient for thehighest sensitivity levels. In some embodiments of access filter 203,the access filter may negotiate the encryption technique to be used in arequest with the client in a manner similar to that which it employs inthe preferred embodiment to negotiate the user identification mode.

Overview of the Administrators' Interface to Access Control Database301: FIGS. 8-12

An access policy defines access in terms of user groups and informationsets; consequently, before an access policy may be defined, theadministrators must define the user groups and information sets; howthat is done is shown in FIG. 8. Defining a user group involves steps803 through 807: first the users are defined, then the user groups aredefined, and then the users are assigned to the proper user groups.Defining information sets involves steps 809 through 813: first theresources are defined, then the information sets are defined, and thenthe resources are assigned to the information sets. When this has beendone for the user group and information set involved in a policy, theaccess policy can be created, as shown at 815. As previously pointedout, the rights to define and determine the membership of user groupsand information sets and to make administrative policy for them aredetermined by the administrative policy, while the right to make accesspolicy for user groups and information sets are determined by the policymaker policy.

As can be seen from the foregoing, the user interface is generally usedto define relationships between two entities or sets thereof. Thegeneral form of the graphical user interface (GUI) for access controldatabase 301 corresponds to that task. The display includes two windows,each of which contains representations of entities that are to bebrought into relationship with each other, and the relationship isdefined by selecting the entities and where necessary, defining therelationship.

Defining User Groups: FIG. 9

FIG. 9 shows the display 901 for populating and defining user groups.Window 903 in the display contains a hierarchical display ofcurrently-defined user groups; window 903 is similar to those used todisplay hierarchies of files in the Windows 95 brand operating systemmanufactured by Microsoft Corporation. In window 903, user groups forwhich the administrative user using display 901 has administrativerights appear in black; the other user groups appear in gray. Above thetwo windows are two button bars 911 and 915. Button bar 911 lists thedisplays available for modifying access control database 301, whilebutton bar 915 lists the operations that may be performed on thosedisplays. Thus, the button label “user groups” in button bar 911 ishighlighted, indicating that display 901 is the one for populating anddefining user groups. With regard to button bar 915, when window 903 isactive, an administrative user with the right to administer a user groupmay modify the user group by selecting it in window 903 and using thedelete button in button bar 915 to delete the user group or the newbutton to add and name a new user group that is beneath the selecteduser group in the hierarchy. When the administrative user clicks onapply button 921, access filter 203 modifies its copy of access controldatabase 301 to conform with what is on display 901 and themodifications are propagated to all copies of access control database301 in the VPN.

Window 909 displays users. A set of user is indicated in the display bythe manner in which the user in the set identified. In this case, theusers are identified by IP addresses and they appear in the display asranges of IP addresses. Button bar 913 indicates the other kinds ofidentifications that can be displayed in window 909. As with window 903,when the window is active, the new and delete buttons can be used to addand delete users. To assign the user(s) specified by a useridentification to a user group, the user of the GUI selects a usergroup, as shown at 917, and a set of identifications, as shown at 919,and then uses the add to group button in button bar 913 to add the setof identifications to the group, as is shown by the fact that the rangeof IP addresses selected at 919 now appears in the hierarchy below theuser group selected at 917. The effect of the operation is to make userswhose sessions have the source IP addresses listed at 917 into membersof the user group R&D, and when the user clicks on the apply button, allcopies of access control database 301 are modified accordingly.

FIG. 10 shows the display 1001 used to define information sets. Here,window 1003 contains a hierarchical list of information sets and window1005 contains a hierarchical list of the available resources. Thehierarchical list of information sets and the hierarchical list ofavailable user groups made in the same fashion as the list of usergroups. Again, information sets and available resources over which theuser of display 1001 has administrative authority appear in black; theother items on the list appear in gray. In window 1001, the availableresources are the Internet and the two locations that make up VPN 201.In a more developed VPN 201, the list of available resources wouldindicate servers at the location, services in the servers, and theinformation items provided by the services. For example, if the serviceprovides a directory tree, the information items contained in thedirectory tree would be indicated by means of a pathname which specifiedthe root of the directory tree and used wildcard characters to specifythe files above the root in the tree. When a resource is added to aserver, the resource may be defined via the 1005 window. Having thusbeen defined, a resource may be assigned to an information set in thesame fashion that a user identification is assigned to a user group.Again, clicking on the apply button causes the changes in display 1001to be propagated to all copies of access control database 301.

FIG. 11 shows the display 1101 used to define policies. Which type ofpolicy is being defined is specified in button bar 1113; as indicatedthere, display 1101 is defining access policy. All of the policydisplays have the same general format: a window 1103 which contains ahierarchical display of user groups, a window 1105 which contains adisplay of a hierarchy of objects for which policy may be defined and apolicy definition window 1107 which contains access policy definitions1108. In the hierarchy of objects, objects for which the user of display1101 has the right to define policies appear in black; the others appearin gray. In display 1101, what is being defined is access policies, sothe objects are information sets.

Each access policy definition has four parts:

an active check box 1117 that indicates whether the access policydefined by the definition is active, i.e., being used to control access;

the user group 1119 for which the access policy is being defined;

the information set 1123 for which the access policy is being defined;and

access field 1121, which indicates whether access is being allowed ordenied and thereby defines the access policy.

Menu bar 1109 and button bar 1115 permit administrators whom the policymaker policy allows to do so to edit, add, delete, and activate ordeactivate a selected policy definition 108. Active check box 1117 ofeach policy definition 1108 permits the administrator to activate ordeactivate the selected policy definition 1108; access field 1121permits the administrator to select either allow or deny as the policy.The delete button in button bar 1115 permits the administrator to deletea selected policy; the new button permits the administrator to make anew policy definition 1108; to do this, the administrator selects a usergroup in window 1103 and an information set in window 1105 and thenpushes the new button. The new access policy definition 1108 appears indisplay 1107, and the administrator can edit the new access policydefinition as just described. To apply a change to access controldatabase 301 and propagate it to all access filters 203, theadministrator clicks on apply button 1125.

Display 1101 also contains a policy evaluator tool which lets theadministrator see how the current set of access policy definitionsdetermines access for a given user group or resource set. When theadministrator clicks on the policy evaluation button in button bar 1113and selects a user group from display 1103, the tool displays theselected user group in blue and all of the information sets in display1105 which the policy definitions permit the user group to access ingreen and the remainder in red; all of the policy definitions which arerelevant to the determination of which information sets may be accessedby the user group are highlighted in the same set of colors. The samething happens if the administrator selects an information set; then theevaluator tool displays the selected information set in blue, all of theuser groups that can access the information set in green and the rest inred, and also highlights the relevant policy definitions. The user canalso select a policy. In that case, the selected policy appears in blueand the user groups and information sets affected by the policy inappear in blue or red, as determined by the policy. The user canadditionally select more than one user group, information set, orpolicy. In that case, the evaluator tool shows each policy that appliesto all of the selected items and the effects of those policies. Theevaluator tool can be turned off by clicking on policy evaluation inbutton bar 1113 and colors and highlights can be turned off inpreparation for a new policy evaluation by clicking on the resetevaluation button in button bar 1115.

FIG. 12 shows the display 1201 used to input information about an accessfilter 203 to access control database 301. Window 1203 shows ahierarchical list of the access filters 203; when the window is active,access filters may be added or deleted using the add and delete buttonsin button bar 1209. Window 1205 is used to input or display informationabout the access filter 203. The display in window 1207 is determined byclicking on a button in button bar 1207; as shown by the buttons,displays in window 1207 can be used to input and view information aboutaccess filter 203's network connections, to input and view informationabout the trust levels of those connections, to scan networks foravailable servers and services, to set up alerts for problems detectedin access filter 203, to specify optional parameter for software, and tospecify the distribution order of access control database 301 changes.The highlighting of alert setup indicates that display 1205 shown inFIG. 12 is the display used to display and establish alerts.

User Interface for Discovering Resources: FIGS. 18 and 24

The users of VPN 201 have an interface for seeing what resources areavailable to them in VPN 201. The interface, termed herein the IntraMapinterface (IntraMap is a trademark of Internet Dynamics, Incorporated),shows each user at least the resources that belong to the informationsets that the user may access according to the access policies for theuser sets the user belongs to. In other embodiments, the IntraMap maytake the sensitivity level of the resource and the trust level of theuser's identification into account as well.

The IntraMap interface is implemented by means of a Java™ applet thatruns on any Java-equipped World Wide Web browser. Using the Web browser,the user can scan the graphical display to find and access resourcesthat are available to the user or to request access to resources thatare not currently available to the user. Access by a user to a resourceis determined by the access policies that apply to the user and theresource. FIG. 18 shows the display 1801 produced by the IntraMapinterface. The left-hand side of IntraMap display 1801 shows a ResourceList 1803; the right-hand side of the display shows a Find field 1807, aSort section 1809, a Services section 1811, and a Description field1813. On-line help for using the IntraMap is available by clicking Helpbutton 1815.

Resource List 1803 shows resources and information available in VPN 201to the user who is using the IntraMap interface. The listing ishierarchical. The user can expand or collapse branches of the “tree” byclicking on the ‘+’ and ‘−’ markers on the branches. Each entry 1804 inthe list includes a name for the resource. The color used to display anentry indicates what kind of access the user has. If the entry 1804 isdisplayed in blue, the user has an active hyperlink to the resource andmay double click on the resource to have it displayed. If it isdisplayed in black, it is also available to the user, but no hyperlinkis available, so a separate application must be used to retrieve it.Resources displayed in gray are not directly available to the user, butif the user selects one, the IntraMap interface opens a dialog box thatpermits the user to send email requesting access to the administratorwho is responsible for access policy for the information set theresource belongs to. The administrator may then modify the access and/oradministrative policies as required to give the user access. Anadministrator may further give a resource the hidden property. When aresource has that property, it will appear in IntraMap interface 1801only if the user belongs to a user group that the access policies permitto have access to an information set that the resource belongs to. If aresource does not have the hidden property, it will always appear inIntraMap interface 1801. Otherwise, it does not appear. A resource mayhave a more detailed description than that contained in its entry 1804.The description is displayed in Description field 1813 when the userselects the resource.

In addition to resource list 1803, IntraMap display 1801 displays twospecialized resource lists at 1805.

What's New 1806 displays the latest information postings from otherswithin the enterprise. If an administrator has given the user access tothe What's New web page, the user may post the URL of a new resourcethere.

What's Hot 1808 displays the enterprise's most popular informationresources, based on how frequently they are accessed.

The service types control at 1811 lets the user filter the resourcesthat are to be displayed in resource list 1803 by the type of servicethat provides the resource. Each service type has a check box in servicetype control 1811. If the box is checked, the service type is includedand the resources associated with this service appear in the ResourceList. Otherwise, the resources associated with this service do notappear in the Resource List.

The IntraMap interface lets the user sort Resource List 1803 byinformation sets, locations, or services. To do this, the user selectsthe way he or she wishes to sort the resource list in sort field 1809.The user may also specify the order in which the categories are used inthe sort. The interface further has a search function. To do a search,the user enters a search string in FIND field 1807. The resource listand the resource descriptions for the resources on it are then searchedin the order specified in sort field 1809. The search simply looks forwhole or partial word matches. It is not case sensitive. The first matchis displayed, and function keys may be used to navigate to othermatches. Of course, if a user has not checked a service type in servicetype field 1811, resources of that service type are not involved ineither sorting or searching.

FIG. 24 shows an implementation 2401 of the IntraMap interface. To theuser of VPN 201, the IntraMap interface appears as a Web page that isone of the resources provided by report manager 209 running on accessfilter 203(c) of FIG. 2. A user in VPN 201 or even the general public(that is, someone who is a member of the Internet user group) may begiven access to the IntraMap interface in the same fashion as he or shemay be given access to any other resource. As will be clear from thefollowing description, the Web page for the IntraMap may be on anyserver in VPN 201. Implementation 2401 has components in workstation2403 used by the user to look at the IntraMap, components in accessfilter 203(I) which is local to work station 2401, and in access filter203(c), which is the access filter upon which report manager 201 runs.Of course, access filter 203(c) may also function as a local accessfilter. Local access filter 203(I) is connected to report access filter203(c) by VPN 201 and workstation 2403 is connected to local accessfilter 203(I) by LAN 213.

As will be explained in more detail later, all access filters 203 have alayered architecture. The bottommost layer is an Internet packet filter2419 that deals only with Internet packet headers. Packet filter 219reads the source and destination addresses in the Internet packetheaders and applies a set of rules to them. As determined by the rules,it either accepts them, discards them, or routes them further in VPN201. The rules also determine how the accepted packets are to be routedwithin access filter 203. The next layer of the architecture is serviceproxies 2427. The service proxies intercept traffic for services such asthe World Wide Web and do access checking on the traffic. If accessfilter 203 provides the service itself or does access checking for aserver that provides the service, IP filter 2419 sends packets intendedfor the service to a service proxy 2427 for the service. The serviceproxy uses access control database 301 to do protocol-level accesschecking for the service. For example, the service proxy for the Webservice may check whether the user making a request for a given Web pagehas access rights for the page. The next higher level is services level2425; if the relevant service proxy permits an access request and theaccess filter is also the server for the service, the request goes tothe service at service level 2425 to be processed. In the case of theWeb page, the service would locate the page and return it to therequester. Two services are involved in the IntraMap: the Web serviceand an IntraMap service. In FIG. 2401, the Web service appears as WebS2423. The proxy for WebS 2423 is WebP 2421; for reasons that will becomeclear in the following, the IntraMap service has only a proxy, IntraMapP2417. Additionally, access control database 301 includes IntraMapinformation 2422, which is an optimized version of the information inaccess control data base 301 that serves as a basis for the IntraMapdisplay.

The chief difference with regard to the IntraMap implementation betweenaccess filter 203(c) and access filter 203(I) is that access filter203(c) includes a World Wide Web page 2410 with a copy of IntraMap Javaapplet 2411. When downloaded from access filter 203(I) to Web client2429 in work station 2403, Java applet 2411 produces requests directedto IntraMap server 2425 and uses the results returned by IntraMap server2425 to produce IntraMap display 1801.

Operation is as follows: to the user of work station 2403, the IntraMapmay appear as a link to a Web page. Thus, to use the IntraMap, the useractivates a link to IntraMap page 2410. Web browser 2429 in workstation2403 responds to the activation of the link as it would to theactivation of any other link to a Web page: it makes a request for thepage and sends it to the server indicated in the link. In the case ofthe link to the IntraMap, the link specifies Web server 2423 in accessfilter 203(c), so the request goes via local access filter 203(I) andVPN 201 to access filter 203(c). As with any other access to a resourcein VP 201, local access filter 203(I) does access checking for theIntraMap page request. Since the request is for a Web page, the checkingis done by Web proxy 2421. In most VPNs 201, IntraMap page 2410 will beaccessible to any user in VPN 201, and access control data base 301 thusindicates that any user with a valid IP source address may accessIntraMap page 2410.

When the request is received in access filter 203(c), IP filter 2419forwards it to Web proxy 2421, which in turn forwards it to Web server2423, which responds to the request by downloading IntraMap applet 2411to Web browser 2429 in work station 2403, where IntraMap applet 2411begins executing in Web browser 2429. During execution, it sends arequest to IntraMap proxy 2427 for IntraMap information 2422. Like allJava applets, IntraMap applet 2411 sends the request to the server thatit is resident on, in this case, access filter 203(c). However, as withany other request from workstation 2403, the request goes by way oflocal access filter 203(I). There, IntraMap proxy 2427 detects that therequest is addressed to IntraMap proxy 2427 in access filter 203(c) andinstead of sending the request on to access filter 203(c), obtainsIntraMap information 2422 from the local copy of access control database 301 in local access filter 203(I), filters it so that it specifiesonly those resources belonging to the information sets to which the usergroups to which the user belongs have access to make to list 2431 andreturns it via LAN 213 to IntraMap applet 2411, which then uses list2431 to make IntraMap display 1801. In making the display, applet 2411applies any filters specified in the request and also sorts the list asspecified in the request. List 2431 not only indicates the resourcesthat are available, but also contains information needed to fetch theresource. Thus, if the resource has a hyperlink, the hyperlink isincluded in the list; if it is a resource for which the user presentlydoes not have access, but to which the user may request access, the listincludes the name and email address of the administrator for theresource.

Details of Access Control Database 301: FIGS: 13-17

In a preferred embodiment of access filter 203, access control database301 is implemented at two levels: one used by the graphical userinterfaces use to manipulate access control database 301 and anotherused in actual access checking. The first level is implemented using theMicrosoft Jet brand database system developed by Microsoft Corporation.The second is implemented using memory mapped files (MMFs) which arecompiled from the first-level data base. The following discussion willdescribe the first-level implementation and explain how the informationcontained in it is used in access checking. In reading this discussion,it should be remembered that actual access checking is done using theMMFs, as will be described in detail later.

As is the case with most database systems, the Microsoft Jet branddatabase system has a schema, that is, a description of the logicalstructure of the database. FIGS. 13-17 are displays generated by theMicrosoft Jet brand database system of the schema for access controldatabase 301. FIG. 13 shows the schema 1301 for the part of the databasethat defines user groups. The display is made up of two elements:representations of classes of tables 1303 in the database andrepresentations of links 1305, which show relationships between tablesbelonging to certain classes of tables. The representation of the classof the table shows the name of the class at 1310 and the data fieldsthat will be contained in each table belonging to the class at 1308.Each table instance has an ID assigned by the database system. The otherdata in the table varies with the class of table. A link is made betweena first table belonging to the first class of tables and a second tablebelonging to the second class of tables by using the ID of the secondtable in the first table and vice-versa. Thus, link 1305 shows thattables of the class User Group. Tree table 1307 can be linked withtables of the class User Groups table 1309. Some links have numbers attheir ends. The numbers indicate the number of the links that the tableat the end the number is located at may have. Thus, the link connectingthe table of class 1309 and the table of class 1307 has the number 1 atthe end for the table of class 1309 and the number at the end for thetable of class 1307, indicating that any number of IDs of instances ofclass 1309 may appear in an instance of class 1307, but only one ID ofan instance of class 1307 may appear in an instance of class 1309.

User Group Tables: FIGS. 13A and B

User group tables 1301 contains a table of class user groups 1309 foreach user group in database 301. Data of particular interest in tablesof class User Groups 1309 include the group name, which is thecharacter-string name of the group, the group description, which is acharacter-string description of the group, and pre-defined information,which indicates among other things whether a user who is a member of thegroup is an administrator, i.e., can make administrative policy, asecurity officer, i.e., can make policy maker policy, or a simple userof information. User group tables 1301 further organizes the user groupsinto a hierarchy—both for the purposes of inheritance and also for thehierarchical display of user groups shown in window 903 of FIG. 9,associate identifications of users with the user groups, and associatealerts with the user groups. The organization into the hierarchy list isdone by means of tables of class User Group Tree 1307. Each table of theclass User Group Tree links a table of the class User Group to a parentuser group (also of the type User Group). Multiple User Group Treetables may exist for a particular User Group table, depending on thenumber of places in which a particular user group appears.

As already mentioned, there are five different ways of identifying usersto an access filter 203: by a range of IP addresses, by afully-qualified Internet domain name, by the identity of the user in theMicrosoft Windows brand operating system, by an authentication token,and by certificate. The table classes for the tables used to identifyusers by certificates are shown as 1321. The table classes for thetables that identify users by a range of IP addresses are shown at 1317;those for the tables that identify users by IP domains are shown at1319; those for the tables that identify users by Windows brandoperating system ID's are shown at 1315; and those for the tables thatidentify users by authentication tokens (labeled as smart card in thefigure) are shown at 1323. The table classes 1325, finally, definetables for the information used in alerts that are related to usergroups. A table of User Group class 1309 may have associated with it anynumber of tables for any of the ways of identifying users. As thisimplies, a given user may be identified in a number of different ways atonce.

In order to perform an access check, access filter 203 must determinewhat user groups the user making the request belongs to. The requestincludes an identification for the user, and the identification is thestarting point for the determination. The tables in user group tables1301 permit access filter 203 to determine from the identification whatuser groups the user belongs to and from those user groups, thehierarchical relations that determine the other user groups the userbelongs to. Assuming that the user is identified by an IP address,access filter 203 begins by finding one or more tables of the IP RangeDefinition class (in 1317) which define ranges of IP addresses whichinclude the user's IP address. Each of these tables has a link to atable of the IP Ranges class (in 1317) which relates the range definedin the IP Range Definition class table to a user group ID, which in turnserves as a link to a table of class User Groups 1309 for the user groupcorresponding to the range of IP addresses. Each of the tables of classUser Group has a link to a table of class User Group Trees, from whichlinks can be followed to the tables of class User Groups for the usergroups from which the user groups specified by the IP addresses inheritaccess rights. Thus, at the end of the process, IP filter 203 haslocated all of the user groups which are relevant for determiningwhether the user may access the resource. Moreover, IP filter 203 knowsfrom the request how the user is identified and can determine from thatwhat level should be assigned to the identification of the user used inthe request. The information in user group tables 1301 is compiled intoMMFs. When a user initiates a session, the user provides a useridentification to the first access filter 203 on the session's path;access filter 203 uses the user identification with the MMFs to make adetermination equivalent to the one explained above. Access filter 203can thus determine for a given user identification whether it identifiesa user that has access, what kind of user identification it is, andtherefore what trust level it has, and which user groups the userbelongs to. User group tables 1301 thus contain all of the informationneeded for the user portion of an access policy 1108.

Information Set Tables: FIG. 14

FIG. 14 shows the schema 1401 for the tables that define informationsets. These tables relate information sets (resource groups in FIG. 14)to the resources that make them up and to the network locations of theresources and also organize the information sets into the hierarchicallist of information sets displayed at 1003 of FIG. 10. Each informationset in access control database 301 is represented by a table of classresource group 1403. Tables of class resource group are organized into ahierarchy for inheritance and display purposes by tables 1419. Therelationship between an information set and the resources that make itup on one hand and the locations in the VPN in which they are stored areestablished by tables of class resource group elements 1407. A table ofclass resource group may be linked to any number of tables of classresource group elements. A table of class resource group elements islinked to any number of tables of the classes Site Elements 1411,Services 1413, and Resources 1409. There is a table of class Resourcesfor every resource represented in database 301. Included in the tableare the resource's ID, its name, the ID for the service that providesit, an ID for a definition of the resource's sensitivity level, adescription of the resource, the email address of the administrator ofthe resource and a hidden flag which indicates whether IntraMap shoulddisplay the resource to users who do not belong to user groups that haveaccess to the resource. The IntraMap interface obtains the informationit needs about a resource from the Resources table for the resource.

The tables of the classes Site Elements and Services, as well as thoseof the classes Sites 1415 and Servers 1417 belong to the classes 1421that describe the locations of information in the VPN. There is a tableof class Sites for every physical location in the VPN; there is a tableof class Servers for every server in the VPN; and there is a table ofclass Services for every service in the VPN. Links in the tables ofclass Site Elements relate sites to servers; links in the tables ofclass Servers relate the servers to the services they offer; and linksin the tables of class Services relate the services to the resourcesthat they host.

In determining what information sets a requested resource belongs to,access filter 203 begins with the information in the request. Therequest is contained in an IP packet, and consequently has a header anda body. In the header there is an IP address which specifies a locationin virtual network 201 and a server at the location, a port number whichspecifies a service on the server, and in the body, the description ofthe resource in the form prescribed by the protocol. For example, if therequest is for a Web page, the description of the resource will be theresource's URL. Access filter 203 uses the IP address to locate a tableof class Sites, uses the link in that table to locate a table of classSite Elements 1411. That table relates the site to the server IDS forthe servers at the site and access filter 203 uses the server IDS tolocate the tables of class Servers 1417 for the site's servers. It canthen use the IP address again to locate the table of class Serverscorresponding to the server specified in the request and can follow thelinks from the Server table to the tables of class Services for theservice and can use the port number from the request to find the properService table. Once it has found the proper Service table, it can followthe links to the tables of class Resources 1409 and locate the Resourcestable corresponding to the resource in the request. From there, there isa link to a table of class Resource Group Elements 1407 which relatesresources to the resource group identifiers for the information setsthey belong to. The resource group identifiers in turn specify tables ofclass Resources Group 1403, and these tables have links to tables ofclass Resource group Tree, from which the hierarchies of resource groupscan be determined to which the resource specified in the requestbelongs. Having done that, access filter 203 has found the resourcegroups that are relevant for determining whether the request should begranted. Resources table for the resource further contains thesensitivity level for the resource. Again, the information ininformation set tables 1401 is compiled into MMFs. When the requestreaches the first access filter 203 in the path between the user and theserver that provides the resource, the first access filter 203 uses theMMF files to make a determination that is the logical equivalent of theone just described. Thus, after examining the MMF files that contain theinformation from User Groups tables 1301 and Information Sets Tables1401, the proxy has determined the trust level of the useridentification, the sensitivity level of the information resource, theuser groups the user belongs to, and the information sets theinformation resource belongs to.

Policy Tables: FIGS. 16A and B

FIG. 16 shows the tables used in access control database 301 to defineaccess control policies; included in these policies are access policies,administrative policies, and policy maker policies:

Access policies relate user groups to resource groups;

Administrative policies relates a user group whose members areadministrators to one of:

d. another user group

e. an information set

f. a resource

g. a location (site) in the VPN

h. an access filter 203 or other server

i. a service

Policy maker policies relate user groups of administrators toinformation sets.

Each policy relates a left-hand side, which is always a table of classUser Groups 1309, to a right-hand side, which, depending on the kind ofpolicy, may be a table of class Resources 1409, a table of classResource Groups 1403 (representing information sets), a table of classSites 1415, a table of class Services 1413, a table of class Servers1417, or a table of class User Groups 1309. Policy tables 1601 thus fallinto three large groups: left-hand tables 1603, policy tables 1605, andright-hand tables 1609. The right to change policies is hierarchical: amember of a user group whose User Group table indicates that it is agroup of a type of Administrators can change access policies asdetermined by the administrative policy for the group. In turn, thoseadministrators may specify other administrative policies related totheir sub-domain.

Corresponding to the three kinds of policies, there are three classes oftables in policy tables 1605: tables belonging to Policies Access class1611, Policies Administer class 1613, and Policies Policy Maker class1619. Tables of all of these classes share a number of features: theycontain the ID of the user group table for the left-hand side of thepolicy, the ID for the table representing the item specified in theright-hand side of the policy, an indication of the policy (accessallowed or denied), an indication of whether the policy is pre-definedand cannot be deleted, and an indication of whether the policy ispresently active. The difference between the classes is what can be onthe right-hand side of the policy, and therefore the links to theentities on the right-hand side; in the case of access policies andpolicy maker policies the right-hand entities are information sets only,and consequently, tables of the Policies Access and Policies PolicyMaker classes contain right-hand links only to tables of the ResourceGroups class, while tables of the Policies Administer class may containright-hand links to in the alternative tables of class User Groups,tables of class Resource Groups, tables of class Sites, tables of classServers, tables of class Services, and tables of class Resources. Therights given the user group specified by the user group on the left-handside of an administrative policy over the sets of entities specified bythe right-hand side vary depending on the kind of entity, as shown inthe following table:

Left- Right- hand hand Side Side Meaning of “allowed” Access User anyMembers of the user group can create administrative po- group licies forthe target or included items. This allows for the delegation ofresponsibilities. User User Members of the user group can administer thetarget user group group group, including nested user groups. Allowedadminis- tration includes deleting, moving, and copying the target usergroup; nesting it in another user group; adding members to it; andnesting other user groups in it. User Infor- Members of the user groupcan administer the inform- group mation ation set, including nestedinformation sets. Allowed ad- set ministration includes deleting,moving, and copying the target information set; nesting it in anotherinformation set; adding members to it; and nesting other informationsets in it. User Site Members of the user group can administer the site,group including elements under it from the Available Resources list (allAccess Filters, servers, services, and resources). Allowedadministration includes deleting and moving the site; adding it to aninformation set; and adding locations and Access Filters to it. Controlover the Intranet location is necessary in order to define new AccessFilters. User Access Members of the user group can administer the Accessgroup Filter Filter, including elements under it from the AvailableResources list (all servers, services and resources). Al- lowedadministration includes deleting and moving the access filter; adding itto an information set; and adding servers or services to it. User ServerMembers of the user group can administer the server, group includingelements under it from the Available Resources list (all services andresources). Allowed administration includes deleting and moving theserver; adding it to an information set; and adding servers or servicesto it. User Service Members of the user group can administer theservice, group including resources under it from the Available Re-sources list (all resources). Allowed administration in- cludesdeleting, moving, and copying the server; adding it to an informationset; adding resources to it. User Re- Members of the user group canadminister the resource. group source Allowed administration includesdeleting, moving and copying the resource and adding it to aninformation set.

The following table describes the rights given administrative usergroups when they appear on the left-hand side of a policy maker policy:

Left- Right- hand hand Side Side Meaning of “allowed” Access UserInform- Members of the user group can manage access policies group tioncontrolling access by any user group to the information set set,including nested information sets. They may also include the informationset and any of its descendants in a further policy maker policy.

As pointed out in the discussion of the Information Set tables above,the proxy that is doing the access checking can use the User Grouptables and the Information Sets tables to find the user groups the usermaking the access request belongs to and the information sets theinformation resource being accessed belongs to and can also use thesetables to determine the trust level of the user identification and thesensitivity level of the information resource. The proxy can thereuponuse the Policies Access tables to find whether any of the user groupsthe user belongs to may access any of the information sets theinformation resource belongs to. If any such user group is found, theuser may access the information set if the request's trust level is ashigh as the information resource's sensitivity level. To determine therequest's trust level, the proxy must determine the trust level of anyencryption technique being used and/or the trust level of the path inVPN 201 that is being used for the access. This information is availablein access filters tables 1701, shown in FIG. 17 and described below. Ifeither the access policies or the access request's sensitivity level donot permit the access, the message is disregarded and any session itbelongs to is dropped. The access checking process is substantially thesame when the request is a request by a user who is a member of anadministrative user group to access database 301, except that whenaccess is permitted, it may result in a modification of the database inaccordance with the rules set forth above. That modification will thenbe propagated to all other access filters 203 in VPN 201.

Server Tables: FIGS. 17A, B and C

FIG. 17 shows the schema for tables that are particularly significantfor the operation of servers in the VPN. There are three kinds ofservers in the VPN:

Plain servers. These are the servers upon which the resources are storedand which execute the services by means of which the resources areaccessed.

Access filters 203.

Policy manager servers. These are access filters 203 that additionallycoordinate and distribute database 301 and/or generate reports aboutoperation and status of the VPN.

An access filter 203 may function additionally as a plain server.

There is a table of class Servers 1417 for every server in the VPN.Information in the table for each server included its ID, name, domainin the Windows NT brand operating system, its Internet name, whether itis an access filter 203 and additionally a policy server, whether accessto it is available only via an access filter 203, and whether it isinside the VPN. If the server is an access filter 203, it additionallyhas an identity that access filter 203 provides to other entities in VPN201 for purposes of authentication and encryption. In a preferredembodiment, the identity is the X.509 certificate for the access filterused by SKIP. The X.509 certificate also includes a public key foraccess filter 203. The public key may belong to one of a number of namespaces; the NSID (name space ID) is an identifier for the public key'sname space; the MKID (master key ID) identifies the public key withinthe name space. Also included in the table is a link to a table of classCertificate Authority 1711 that indicates the certificate authority thatissued the X.509 certificate for the access filter. Of course, serversother than access filters may also have X.509 certificates, and in thatcase, their Server tables will have the server's NSID and MKID.

Every plain server in the VPN has one or more services running on it.For example, an FTP service provides access to files (the resources) onthe server according to the file transfer protocol of the TCP/IPprotocol suite. Each table of class Servers 1417 for plain servers haslinks to a group of tables that define the services and resourcesavailable on the server. As shown at 1719, these tables include tablesof class Services 1413, which represent the services, tables of classResources 1409, which represent the resources available via theservices, and tables of class Service Definitions 1715 which define theservice.

The remainder of the tables for which FIG. 17 gives the schemas containinformation that is used by access filters 203. The tables whose classesare shown at 1705 contain information used by access filters 203 thatare policy managers to distribute database 301 and/or to generatereports; the tables whose classes are shown at 1717 contain informationabout optional parameters for the software being run by a given accessfilter 203; those whose classes are shown at 1709 contain informationabout the proxies and other software modules that access filters 203 useto do protocol-level access checking in access filter 203; and thetables at 1707 contain information about trust and sensitivitydefinitions for identifications of users and kinds of encryption.

The tables indicated by the reference number 1708 contain informationabout the VPN to which access filter 203 belongs. Access filter 203 usesthis information to route sessions and also to determine the trust levelof the path being used for a given session. Routing table class 1721defines tables that list the current routes to all networks accessiblefrom access filter 203. It is automatically updated as those routeschange. Attached Network class 1723 defines tables that indicate foreach access filter 203 the networks that access filter 203 is presentlyattached to; tables of that class contain links to tables of classNetwork Definition, which in turn contain a link to a definition intrust definitions 1707 which indicates the trust level of the network.The last class in this group is Point to Point Connection 1713, whichdefines tables that describe connections between access filters 203accessible via the VPN. There is a table for each combination of sourceand destination access filter 203 and a link to a trust definition thatspecifies the trust level of the path between the source and destinationaccess filters 203. The trust level in this table is based on theencryption technique used for messages traversing the path.

As previously explained, the User Group tables 1301 and the InformationSets tables 1401 provide the information needed by access filter 203 todetermine whether the access policies of tables 1601 permit the accessand also provide information about the sensitivity level of the resourcebeing accessed. Access filters tables 1701 additionally provide theinformation needed by access filter 203 to determine the minimum trustlevel of the path in the VPN being taken by the session and the trustlevels of the available encryption algorithms. Thus, if access filter203 determines that a given user wishing to access a given resourcebelongs to a user group which has the right to access the informationset to which the given resource belongs and that the authenticationlevel used for the user's identification is no lower than that requiredfor the resource's sensitivity level, access filter 203 can furtherdetermine whether the trust level of the path is sufficiently high, andif it is not, access filter 203 can raise the trust level the necessaryamount by selecting an encryption algorithm with the required trustlevel and encrypting the session.

Available Information Tables: FIG. 15

FIG. 15 shows the schema for available information tables 1501. Thetables are used by filter 203 to produce available resources display1005, shown in FIG. 10. The table classes shown at 1502 relate eachserver to its services and to the resources provided by the services.The table classes shown at 1504 organizes the available resources into ahierarchy for inheritance purposes and are also used to produce thehierarchical list shown at 1005, and by following the links from theSite Elements tables to the Servers tables, access filter 203 candetermine the hierarchy of sites, servers, services, and resources. Thetable classes at 1503, finally, establish a distribution tree of accessfilters 203. As will be explained in more detail later, when accesscontrol database 301 is modified, the tree defined by those tablesdetermines the order in which modifications are distributed to theaccess filters.

Modifying Access Control Database 301: FIG. 19

As previously mentioned, each access filter 203 has an exact duplicateof the copy of access control database 301 belonging to master policymanager 205 in access filter 203(a) of FIG. 2. FIG. 19 shows how thatcopy of access control database 301 is modified and how themodifications are distributed from access filter 203(a) to the otheraccess filters 203.

FIG. 19 shows access filter 203(a) with master policy manager 205 andanother access filter 203(i) at which an administrator using aworkstation is modifying access control database 301. The messages 1909needed to distribute and synchronize the modifications are encryptedusing SKIP and sent via VPN 201 using a protocol called the privatecommunications service (PCS). Each of the access filters has a number ofcopies of access control database 301. Any access filter 203 has at aminimum two copies: live database (LDB) 1907, which is the databasecurrently being used to do access checking, and mirror database (MDB)1905, which is a copy of the database that can be switched in to be usedin place of live database 1907. Thus, access filter 203(a) has an MDB1905(a)and an LDB 1907(a)and access filter 203(i) has MDB 1905(i)and LDB1907(i).

If an access filter 203 is being used by an administrator to modifyaccess control database 301, then it will additionally have at least oneworking database (WDB) 1903. The working database is a copy of thedatabase that is not being used to control access and therefore can bemodified by the administrator. The administrator does so using aworkstation or PC connected via a network to the access filter. Theworkstation or PC displays the administrative graphical user interfacedescribed above, and the administrator uses the GUI to make the changesas enabled by administrative policies. The changes may affect any aspectof the information stored in access control database 301. As indicatedabove, where the changes are changes in access or administrativepolicies, the administrator can use the policy evaluation feature to seethe effect of the changes. When the administrator is satisfied with thechanges, he or she clicks on the apply button and the changes aredistributed to all of the access filters and incorporated into eachaccess filter's live database.

The process of updating all of the live databases is called databasesynchronization and distribution. The process has three phases:

First, the modifications are sent from the access filter 203 where theywere made (here, access filter 203(i)) to access filter 203 to which themaster database belongs (here, access filter 203(a)).

There, the changes are incorporated into the master database. This isdone by incorporating the changes into mirror database 1905(a), thenswapping live database 1907(a)and mirror database 1905(a), and thenchanging the new mirror database 1905(a).

Then, the changes are distributed from the Master Policy Manager toother Access Filters.

At each access filter 203, synchronization is done in the same fashionas with access filter 203(a). The order in which the changes are made inthe access filters 203 of VPN 201 is determined by distribution tree1511, which in turn is set up using filters display 1201. The accessfilter 203 with master policy manager 205 is always the root of thetree. By default, the first access filter 203 installed in VPN 201 hasmaster policy manager 205. As other access filters 203 are installed,they are added to the tree as children of the Master Policy Manager.

The Master Policy Manager distributes changes to its childrensequentially. As each child access filter 203 receives its distribution,it then distributes to its children. This means that a shallowdistribution tree with many branches off the top level will complete adistribution cycle faster than a deep distribution tree with fewbranches off the top level. An administrator with the proper access canreconfigure the distribution tree to make distribution more efficient.

If two administrators have modified the same piece of information (forexample, an access filter definition) in different working data base1903, a synchronization conflict can occur. When this happens, masterpolicy manager 205 decides which modification to incorporate into accesscontrol database 301.

Optimizing Access Control Database 301: FIGS. 21 and 23

Although appropriate for persistent storage and use by administrationGUI 1915, database 301 is not optimized for use in real-time accesschecking. As will be explained in more detail below, access filter 203optimizes the data in database 301 that is required for run-time accesschecking and to make the display for the IntraMap. It does theoptimization each time a new copy of database 301 is received in accessfilter 203. In its optimized form, database 301 is a set of MemoryMapped Files (MMFs) in which the access policy information is stored ina form which permits quick access. The MMFs are so called because theyare generated as normal files, but then attached to a program's memoryspace and accessed by means of memory operations instead of fileoperations. A further optimization is achieved by using the MMF files togenerate rules that are used to do low-level filtering of messages by IPsource and destination addresses and port numbers for which access isallowed or denied.

FIG. 21 shows an example MMF file 2303. The MMF file in question isDBCertificatesbyUserGroupFile 2101, which maps the certificate matchingcriteria used to identify certificates that belong to particular usergroups to identifiers in database 301 of records for the user groupsspecified by the certificate matching criteria. File 2101 thus permits aproxy that has the certificate that identifies the source of a messagethat has been encrypted using SKIP to quickly determine the user groupsthat the user identified by the certificate belongs to. In the preferredembodiment, the certificate matching criteria are the O, OU, and CAfields of the X.509 certificate.

All MMF files 2303 have the same general form: there are two main parts:a header 2103 which contains the information being mapped from and adata part 2105 which contains the information being mapped to. Header2103 contains a list of entries 2107. Each entry contains a value beingmapped from (in this case certificate matching criteria (CMC) 2109) anda pointer 2111 to a record in data 2105 which contains the informationbeing mapped to (in this case, a list 2115 of identifiers 2113 indatabase 301 for the user groups that the user identified by CMC 2109belongs to). The entries in header 2103 are sorted by the informationbeing mapped from (here, CMC 2109), so that standard fast searchingalgorithms can be used to locate an entry 2107 corresponding to a givenset of certificate matching criteria.

FIGS. 23 A, B, and C provide a complete list of the MMF files 2301 thatare employed in one implementation of access filter 203. Therelationship between these files and the tables of database 301 will beapparent from the descriptions of the contents of the files provided inthe table. Each MMF file 2303 is represented by an entry in the tablewhich indicates the file's name and its contents. The files aresubdivided into groups 2311, 2313, 2319, 2321, 2323, and 2422. Files ofparticular interest are DBUsersFile 2307 and DBResourcesFile 2309, whichdescribe policies, DBCertificatesByUserGroupFile 2101, which is the MMFfile shown in detail in FIG. 21, DBResourceIDbyServiceIDFile 2315, whichrelates URLs of resources to resource IDS, DBResourcesbyResourceIDFile2317, which relates resources to resource groups, and DBTrustTableFile2325, which implements SEND table 601. Moreover, the following files areused to compile rules:

DBServerIDByNameFile

DBIPAndTypeByServerIDFile

DBServicePortToProxyPortFile

DBAttachedNetworksByServerIDFile

DBRoutingTableFile

DBRoutingTablebyServerIDFile

The files in IntraMap information 2422, finally, are filtered to makelist 2431, which is then downloaded to the client for use by IntraMapapplet 2411.

Details of Access Filter 203: FIG. 20

FIG. 20 is a block diagram of the architecture 2001 of an access filter203. In the implementation shown in FIG. 20, all of the components ofaccess filter 203 other than NIC cards 2013 are implemented in software.The software of the implementation runs under the Windows NT brandoperating system manufactured by Microsoft Corporation. The softwarecomponents fall into two broad classes: those that run as applicationsprograms at user level 2003 of the operating system and those that runat the kernel level 2005 of the operating system. In general, theprograms that run at the kernel level do IP-level access checking andencryption and authentication, while those that run at the user level doapplication-level access checking. Also included in the user-levelcomponents are software that manages access control database 301 andsoftware that produces the MMFs and rules for IP-level access checkingfrom access control database 301. The following discussion will beginwith the kernel components, continue with the user-level componentsrelated to access control database 301, and will then deal with thecomponents for protocol-level access checking.

Kernel-Level Components

Network Interface Cards (NICs) 2013: These are the ethernet and tokenring cards installed in access filter 203. Three network cards aretypically configured. One is configured for the interface to theInternet, to a wide area network (WAN) 2011, or to a network connectedto another access filter 203. Another is configured for interface 2007to all client computers and a third is configured for interface 2009 tothe servers providing TCP/IP services. If there is no need for an accessfilter 203 to be interposed between clients and servers, there may beonly two NICs 2013, one to WAN 2011 and the other to a LAN. There willbe no need for the access filter to be interposed if no servers exist ataccess filter 203's location or if it is acceptable for all localclients to have access to all local information resources.

SHIM 2017: at installation time, a shim software module is insertedbetween two levels of the Windows NT brand operating system (the NDISand TDIS levels). This causes all traffic for particular protocols topass through SHIM 2017. In the implementation, all traffic for TCP/IPprotocols pass through SHIM 2017, while non-TCP/IP protocol traffic goesdirectly from the NIC to the appropriate other kernel modules. SHIM 2017invokes SKIP module 2021 as required to process the TCP/IP protocoltraffic.

SKIP module 2021: All IP network traffic is sent through SKIP module2021. If an incoming packet is not SKIP type, i.e., does not require theauthentication and decryption services performed by SKIP, then SKIPmodule 2021 passes it to IP filter module 2019. Similarly, if anoutgoing packet is not to be encrypted, then SKIP module 2021 sends itdirectly to the proper NIC 2013 for transmission. With SKIP-typepackets, authenticator 2024 in SKIP module 2021 serves to authenticate asession and encryptor/decryptor 2022 serves to encrypt and decryptinformation at a session level. Both authentication andencryption/decryption may be done with an arbitrary number of otheraccess filters 203, servers that employ SKIP, and clients that employSKIP. Authentication and encryption algorithms are set by IP filtermodule 2019 for outgoing packets based on SEND parameters or arespecified within incoming packets.

SKIP module 2021 maintains enough state information for each other sitethat it talks to so that it can maintain high-speed operation for mostSKIP-type packets. Packets are sometimes ‘parked’ while additionalprocessing (shared secret and temporary key calculation) is performed.‘skipd’ module 2037 in user space 2003 performs this extra processing.

IP Filter 2019: The IP filter operates on a set of rules that the rulescompiler, a component of database service 2029, makes from the accesspolicies in access control database 301. The basic functions of IPfilter 2019 are to:

a. Pass traffic up to the TCP/IP stack.

b. Block traffic—explicitly drop traffic for specific IP addresses andaccording to special rules for emergency conditions.

c. Drop traffic—implicitly drop traffic that neither matches any rulesnor is allowed by any policies.

d. Proxy traffic—rather than deliver traffic to the indicateddestination, route it to a proxy application on the current machine.

e. Perform network address translation—change potentially illegalinternal IP addresses to legal ones.

f. Pass decisions off to pr_ipf (discussed below) upon establishing anew session for which access control cannot be decided strictly by therules. Typically, this is for sessions that may be allowed by policiesor by the VPN tunneling features described previously.

IP filter 2019 performs these functions based on the followinginformation:

Rules generated by the rule compiler;

Source and destination IP address and port;

Encryption, or lack of it, on the incoming packet; and

Desired encryption and authentication on outgoing packets.

Components Having to do with Database 301

Shared Directory 2028: VPN 201 uses a single access control database 301that is kept resident in each and every access filter 203. All versionsof database 301 in a given access filter 203 are maintained in shareddirectory 2028. Shared directory 2028 also contains each access filter203's log files.

Private Connect Service (PCS) Module 2025: PCS module 2025 providesaccess filter-to-access filter communications in VPN 201. All suchcommunications go through the PCS. The PCS has its own IP port numberand its messages must be encrypted. The particular functions carried outby means of PCS messages are:

Distribution tree management;

Distribution and synchronization of database 301;

Retrieval and distribution of routing table 1721;

Retrieval of Windows domain and user information;

Network scanning;

Retrieval of log contents; and

Transfer of files used by reporting and other subsystems.

ISDB Manager 2027: ISDB manager 207 manages database 301. It and the PCSare the only interfaces to the copies of database 301 in each accessfilter 203. It contains the software used to read and write all tablesin the copies of database 301.

DB Service and Rules Compiler 2029: DB Service 2029 produces MMF files2301. It does so each time a new copy of database 301 is received inaccess filter 203. It utilizes the functions provided by ISDB Manager2027 to read live database 1907(I) for a given access filter 203(I) andgenerate the MMFs 2301. A component of DB service 2029 is the RuleCompiler, which generates rules for use in the IP filter module fromrelevant ones of the MMFs 2301. The rules specify IP sources,destinations, and port numbers for which access is allowed or denied.The Rule Compiler exists as both a DLL and an application program thatsimply invokes routines in the DLL. In normal operation, the routines inthe DLL are invoked by the DB Service whenever a modified database 301is received in access filter 203(I) from master policy manager 205. Theapplication program is used in special modes during the installation andbootstrapping process.

Memory Mapped Files (MMFs)2301: As already explained, the MMFs 2301 aredata files generated by DB Service module 2029 and utilized by a numberof other modules in access filter 203. The files are designed to makethe following operations as efficient as possible:

Map from user identification to user group(s);

Map from information resource to information set(s);

Find policies that are associated with user groups; and

Find policies that are associated with information sets.

Components Related to Authentication

Evaluator 2036: Evaluator 2036 is a set of DLLs that are used by eachproxy in proxies 2031. Evaluator 2036 provides the following functionsto the proxies:

Prompting the user for further in-band or out-of-band identificationinformation;

Obtaining out-of-band authentication information from the AuthenticationTool Service (ATS);

Obtaining the certificate associated with the current user from SKIPd;

Reading the MMFs 2301 and determining whether the access policies permitthe user to access the resource; and

Implementing the trust/sensitivity calculations for the path if accessis otherwise allowed, including deciding whether access may be allowedvia the path and if so, what encryption and authentication is needed andwhich access filter is nearest the server. These functions are performedby a component of evaluator 2036 termed the VPN manager.

Authentication Tool Service/User Identification Client (ATS/UIC) 2039and 2041: ATS 2039 is the server in a client-server application thatgathers and authenticates user information. ATS 2039 runs on thecomputer upon which the other components of access filter 203 arerunning. The client part is UIC 2041, which runs on Windows-basedclients. ATS 2039 and UIC 2041 are the mechanism by means of whichaccess filter 203 obtains out-of-band authentication information. ATS2039 and UIC 2041 communicate by means of a session which is separatefrom the session being authenticated. ATS 2039 gathers and caches theauthentication information it obtains from the UIC clients and providesit to Evaluator 2046. The cached information from the clients includes

Windows ID;

Identity Certificates; and

Authentication token ID's.

SKIPd 2037:

Most of SKIPd's functions are in support of SKIP 2021. Those functionsinclude:

Exchange of certificate information with other communications partners.This is done through the use of the Certificate Discovery Protocol(CDP).

Calculation of the Diffie-Hellman shared secret. This shared secret iskey to the operation of SKIP. This calculation can take a considerableamount of time and is saved to disk in an encrypted form.

Calculation of the transport key used to encrypt the session. These keyslast for a period of time or amount of data.

In addition, SKIPd will provide certificate matching criteria to theEvaluator(s) for use in user identification.

Proxies 2031

As previously explained, a proxy is software in filter 203 thatintercepts traffic for a particular protocol. The proxy ‘understands’the protocol that it is intercepting and can obtain the informationrequired to identify the resources being accessed and/or to authenticatethe user from the messages that are being exchanged during the session.All of the proxies but SMTP receive messages on ports other than thestandard ports for their protocol, with the IP filter redirectingmessages using a given protocol from its standard port to itsnon-standard port. The proxy provides the information it has obtainedfrom the session to evaluator 2036 to decide whether the user has accessto the information resource. If the user does have access, access filter203 forwards the incoming messages to the server to which they areaddressed and the messages are processed further in the server by theservice for the protocol. In the following, each of the protocolsemployed in a preferred embodiment is discussed; of course, otherembodiments may include proxies for other protocols.

Pr_ipf: The majority of network traffic occurs over a small number ofprotocols for which there are proxies in access filter 203. However,even where there is no proxy, an access decision must be made. In somecases, the decision can be made at the kernel level by IP filter 2019;when it cannot be, IP filter 2019 provides the traffic to pr_ipf, whichobtains whatever information relative to user identification andinformation resources it can from the traffic and passes the informationto evaluator 2036 to determine whether access should be granted. Pr_ipfis not truly a proxy, since it only makes an access determination for IPfilter 2019 and does not pass any traffic to standard protocol software.

FTP: The FTP proxy handles TCP/IP packets for the File TransferProtocol. In a present embodiment of VPN 201, access control is onlyenforced to the account (logon) level; in other embodiments, access maybe controlled to the file access level. During the FTP logon portion ofthe protocol, the proxy determines the server and account being accessedand provides this information to evaluator 2036 to determine whether theuser belongs to a user group whose members may access the informationsets corresponding to the account. The proxy further handles the in-bandauthentication using tokens in interactions with the user that arespecified in the FTP protocol.

FTP is actually a very complex protocol, involving both an active andpassive mode (used in Web browsers and some automated FTP clients). Inaddition, FTP data transfers utilize a second, dynamically determinedTCP session. This requires a special interface between the FTP proxy andIP Filter 2019 so that the FTP proxy can indicate to IP filter 2019 thatit should allow the second session.

HTTP: The HTTP proxy is built from the source code for the public domainCERN implementation of HTTP and contains all of its caching logic. Theproxy uses evaluator 2036 to check each access to a URL. No in-bandauthentications are performed with HTTP.

Telnet: The Telnet resource is only controlled to the server level dueto the non-standardized nature of Telnet logins. The Telnet proxy isonly used in order to provide additional in-band authentications. It isthe simplest of the true proxies.

NNTP: The NNTP (Network News Transfer Protocol) is used to control bothnews feed and news reading operations. During the feed operation, theNNTP proxy watches for uuencoded messages. These are binary messagesthat have been translated into ASCII text for the purposes oftransmission. Such messages are often broken up into multi-part messagesto keep them to a reasonable size. The NNTP proxy caches all parts ofbinary messages. For each such message, if that message is the last partthat will complete a multi-part message, then the entire multi-partmessage is assembled and anti-virus 2033 checks it for viruses asdescribed in more detail below. During the news reading operation,access is protected to the news group level. As in other proxies,evaluator 2036 is used to determine if the current user may access thenews group.

Real Audio: The Real Audio proxy allows clients to access real audioservers that are protected at the server level only. The real audioprotocol utilizes a standard TCP socket connection to establish asession, but then uses a return UP channel. As with FTP, the real audioproxy has an interface to IP filter 2019 that permits it to indicate toIP filter 2019 that the return UP channel is allowed.

SMTP: The SMTP (Simple Mail Transfer Protocol) differs from the otherproxies in that the IP Filter's proxy rules are not used to redirecttraffic to the SMTP proxy. Whereas the other proxies ‘listen’ on anon-standard port, the SMTP proxy listens on the standard port (25) andthen makes its own connections to the standard SMTP server software. Theaccess policies in database 301 must explicitly allow this access.

IntraMap: When a user specifies the URL for the IntraMap, report manager209 downloads the IntraMap Java applet and the downloaded appletattempts to make a connection back to a socket of the access filter 203that has report manager 209. IP filter 2019 of local access filter203(I) intercepts the attempt to make the connection and provides it tothe IntraMap proxy on local access filter 103(I) The proxy responds toqueries from the applet by finding the answers in the local copy ofdatabase 301 and returning the answers to the applet, with all answersbeing filtered to reflect the user's access rights. The IntraMap proxyis not a true proxy in that the entire connection is always completelyserviced by the instance of the IntraMap proxy that intercepts theconnection.

Anti-Virus Module 2033

Anti-virus module 2033 in a preferred embodiment is a set of DLLsprovided by Trend Micro Devices, Inc., Cupertino, Calif. In otherembodiments, anti-virus modules from other sources may be used.Anti-Virus module 2033 checks all data entering VPN 201 for viruses. Inorder to provide the user with feedback on the progress of the transferand to prevent the user's client program from timing out, the data istransferred to the client and is copied at the same time into atemporary file used for virus checking. The last portion of the data,however, is not sent to the client until after virus checking iscomplete. As soon as the last portion is in the temporary file, thetemporary file is checked for viruses. If no viruses are detected, theremainder of the data is sent to the client. If a virus is found, thenthe transfer is aborted. In a present embodiment, the user is notifiedof a failed transmission. If an administrator has so specified, an alertmay be sent to the administrator.

Launch, Log, Alert and Reports 2027

The components of this module perform the following functions:

Launch—controls the initial sequence of startup tasks that takes placeon an access filter 203 when VPN 201 is established.

Logs—a DLL that provides a standardized logging interface.

Alerts—a standalone program that watches all of the NT logs, looking foralert conditions specified in database 301. The method by which an alertis delivered is specified using the GUI for defining alerts.

Reports—a subset of the logs are forwarded to a special report log,concentrated into a database and later forwarded to Report Manager 209.

Administrative Graphical User Interface 1915

The GUI may run on access filter 203 or on any computer having a 32-bitWindows brand operating system that is attached to access filter 203.Whether the GUI runs on access filter 203 or on an attached system, itutilizes ISDB MANAGER 2027 to read from and write to a working copy 1903of access control database 301. All necessary modifications to accesscontrol database 301 are made through GUI 1915. An ‘apply’ operation inthe GUI is sent as a signal to PCS 2025, which responds to the signal bystarting the previously-described distribution and synchronizationoperation.

Detailed Example of Operation of Access Filter 203: FIGS. 5 and 22

In the following, the end-to-end encryption example of FIG. 5 will beexplained in detail. In that example, a roamer 503 whose PC is equippedwith SKIP is accessing a SKIP-equipped server 407 inside a site on VPN201. When roamer 503 was set up to access VPN 201, it was set up to doso via access filter 403(3) using a particular type of encryption. Here,it will be assumed that the type of encryption being used by roamer 503has a trust level of “secret” and that the user wishes to access a Webpage on server 407 that has a sensitivity level of “secret”. Since whatis being accessed is a Web page, roamer 503 is using the HTTP protocolfor its session with the HTTP service on server 407. Since roamer 503,the access filters 203 in VPN 201, and server 407 are all equipped withSKIP, they are all provided with their own public and private keys. At aminimum, roamer 503 also has the certificate and public key for accessfilter 403(3) to which it directs messages for servers internal to VPN201; access filter 403(3) has the certificate and public key for roamer403 (or obtains them using the Certificate Discovery Protocol); allaccess filters 203 in VPN 201 have or can get each others' public keysand the public keys for servers in VPN 201 that are equipped with SKIP.Additionally, each access filters 203 in VPN 201 knows the IP addressesof all of the other access filters 203 and servers in VPN 201.

All of the messages which are sent and received as part of the HTTPsession between roamer 503 and server 407 are encrypted andauthenticated by SKIP. FIG. 22 shows the form taken by such a SKIPmessage 2201. The SKIP message is made by SKIP software on the systemwhich is the source of the SKIP message. SKIP message 2201 shown here isfrom roamer 503. Its main components are:

Outer IP header 2203: Outer IP header 2203 is used to deliver the SKIPmessage to access filter 403(3). Contained in outer IP header 2203 are asource IP address 2209 for roamer 503 and a destination IP address 2206for access filter 403(3). Destination address 2206 used by roamer 503was set to specify access filter 403(3) when roamer 503 was set up toaccess VPN 201. Source IP address 2209 may be dynamically assigned toroamer 503 by the Internet service provider that roamer 503 uses toconnect to Internet 121. Outer IP header 2203 further contains a messagetype (MT) field 2208 which specifies that the message is a SKIP message.

SKIP header 2205: SKIP header 2205 contains the information needed todecrypt SKIP message 2201 when it is received. SKIP header 2205 containsat least a destination NSID 2215 and destination MKID 2213 for thedestination's certificate, that is, the certificate for access filter403(3), and the source NSID 2219 and source MKID 2217 for the source'scertificate, that is, the certificate for roamer 503. In addition, SKIPheader 2205 contains identifiers for the algorithm used to authenticatethe message (MAC ALG 2226) and the algorithm used to encrypt the message(CRYPT ALG 2225), as well as an encrypted transport key for decryptingthe message (Kp 2223) and an identifier 2224 for the algorithm used todecrypt the transport key.

Authentication header 2211: Authentication header 2211 contains a MAC(message authentication code) 2221, which is computed according to theMAC algorithm identified in field 2226 and which is used by accessfilter 403(3) to verify that the message arrived without tampering.

Encrypted payload 2227: Encrypted payload 2227 contains the encryptedmessage which roamer 503 is sending to server 407, including IP header2331 for that message and encrypted message 2229. IP header 2331 has theIP address for server 407 and the port number for the HTTP protocolservice. Encrypted payload 2227 can be decrypted by using Kp 2223 withthe decryption algorithm specified by CRYPT ALG 2225.

Handling SKIP Message 2201

SKIP message 2201 arrives on Internet interface 2011 of access filter403(3). Processing of the message begins at the SHIM level in kernel2005. SHIM 2017 sends all incoming traffic to SKIP 2021, which in turnrecognizes from MT field 2208 that the message is a SKIP message. Todecrypt and authenticate the message, SKIP needs to decrypt Kp, and todo that it provides SNSID 2219, SMKID 2217, DNSID 2215, and DMKID 2213to SKIPd 2037, which uses the IDs to retrieve the certificates forroamer 503 and access filter 403(3) from SKIPd 2037's certificate cache.If a certificate is not there, SKIPd 2037 uses the CDP protocol to fetchthe certificate. The information in the certificates is then usedtogether with access filter 403(3)'s private key to create a sharedsecret value, which is then used to decrypt transport key Kp 2223 and toproduce two internal keys, Akp and Ekp. SKIP securely saves the sharedsecret for use with future messages, since its computation takes asignificant amount of time. Next, a MAC is computed for the entirereceived message and the Akp is used with MAC 2221 and MAC ALG 2226 toverify that entire message 2201 has not been tampered with. If that isthe case, the key Ekp is used to decrypt encrypted payload 2227 torecover the original message from roamer 503. Decrypted payload 227 isthen provided to IP filter 2019, which applies its rules to the sourceIP address, destination IP address, and port number of IP header 2231.If no rule denies access, IP filter 2019 follows another rule andredirects the unencrypted message together with SNSID 2219 and SMKID2217 to the port for the HTTP proxy. IP filter 2019 uses theDBServicePortToProxyPortFile of MMFs 2301 to find the port in question.

Processing continues at the application level in user level 2003 of theoperating system. The HTTP proxy has in hand the IP address of theserver, the port number of the service, the URL for the Web page, thecertificate belonging to the user of roamer 503, and the encryptionmethod used to encrypt the message. It will use evaluator 2036 todetermine the following from the MMF files 2301:

the user groups that the user represented by the certificate belongs to;

the information sets that the Web page belongs to;

whether there is an access policy that permits at least one of the usergroups to access at least one of the information sets; and

whether the trust level of the message is at least equal to thesensitivity level of the Web page.

Beginning with the first of these tasks, evaluator 2036 receives theNSID and MKID for the certificate and uses the certificate matchingcriteria from the certificate with the DBCertificatesByUserGroupFile toobtain the identifiers for the user groups the user sending the messagebelongs to.

Evaluator 2036 determines the information sets by taking the IP addressof the server, the port number of the service, and the URL for the Webpage and using the IP address with the DBServerIDByIPFile to determinethe server that contains the Web page, the port number with theDBServiceIDByPortFile to determine the service on the server thatprovides it, and the URL with the DBResourceIDbyNameFile to get theidentifier for the resource in database 301, and then uses theDBResourcesByResourceIDFile to get the identifiers for the informationsets that the Web page belongs to.

With the identifiers in database 301 for the user groups and informationsets in hand, evaluator 2036 uses the DBResourcesFile to determinewhether there is an access policy which permits any of the user groupsthat the user belongs to access any of the information sets that the Webpage belongs to. In so doing, it may only consider user groups whosemembership is determined using modes of identification whose trustlevels are sufficient for the resource's sensitivity level. TheDBResourcesFile maps each information set identifier to a list of theuser groups for which there are access policies involving that resourceset. For each user group, the DBResourcesFile further indicates whetherthe policy allows or denies access. Evaluator 2036 uses theDBResourcesFile to determine for each information set in turn that theWeb page belongs to whether the list of user groups for which there areaccess policies with regard to the information set includes one of theuser groups to which the user belongs. If there is an access policy forany of the user groups that denies access, the evaluator indicates tothe HTTP proxy that access is denied; if there is no access policy forany of the user groups that denies access and at least one that allowsaccess, the evaluator indicates to the proxy that access is allowed; ifthere is no access policy of any kind for any of the user groups, theevaluator determines if there is at least one certificate or token baseduser group that has an allow policy for the resource. If so, and therequesting client has a UIC running, then the UIC is contacted to askthe user for additional identity information; if additional identityinformation comes back, the process described above is repeated.Otherwise, the evaluator indicates to the HTTP proxy that access isdenied.

Of course, evaluator 2036 will also deny access if the access requestdoes not have a trust level equal to the sensitivity level of the Webpage. Evaluator 2036 obtains the sensitivity level of the Web page fromthe DBResourcesByResourceIDFile, the trust level of the useridentification from DBTrustAuthenticationsFile, and the trust level ofthe encryption method from the DBTrustEncryptionsFile. Since SKIP hasencrypted the message with a method that has the “secret” trust level,the trust level of the path through the network is not of concern inthis example. To determine whether the trust levels for the useridentification and the encryption method are sufficient for thesensitivity level of the Web page, Evaluator 2023 uses theDBTrustTableFile, which effectively implements SEND table 601. If thetrust levels are sufficient, Evaluator 2036 indicates to the proxy thatthe access is allowed.

Once the proxy has confirmed that access is to be allowed to theinformation resource specified in the message, the proxy originates anew session to the actual service, the HTTP service on server 407. Proxy2031 sends a special message to IP filter 2019 telling it to allow thespecific session through, since otherwise this session would probably beblocked by rules or sent again to a proxy. The message to IP filter 2019also includes information about the encryption needed for the newsession, which in this example is that the session should be encryptedto the final access filter 403(5) and should use encryption suitable forthe data sensitivity level, which is secret. When IP filter 2019encounters the new session, it finds that it matches the criteriaspecified by proxy 2031, so it passes the session to SKIP. Sinceencryption is needed for this session, the message will be reencrypted.SKIP 2021 creates a SKIP message 2201 in the same fashion as describedabove, except that:

Outer IP header 2203 for the message specifies access filter 403(3) asthe source of the message and access filter 403(5) as the destination;

SKIP header 2205 has SNSID 2219 and SMKID 2217 for access filter 403(3)and DNSID 2215 and DMKID 2213 for access filter 403(5), and the othervalues in header 2205 are also those required by the fact that thesource and destination for the message are now access filter 403(3) andaccess filter 403(5);

Encrypted payload 227 is the same as before (except that it has beenencrypted using a different key) and MAC 2221 is produced as requiredfor entire new message 2201.

As the proxy is relaying the message it is also watching for filetransfer types that might contain viruses. When it encounters one, itapplies anti-virus software 2033 to these files. If a file contains avirus, the proxy fails to deliver the complete file, thereby renderingthe virus harmless. If access control database 301 so indicates, theproxy sends an alert when anti-virus software 2033 detects a virus.

As new SKIP message 2201 is received at access filter 403(5), it ispassed to SKIP 2021, where it is authenticated and decrypted asdescribed previously. By the same mechanism as described above withregard to access filter 403(3), IP filter 2019 on access filter 403(5)recognizes that the message is destined for the HTTP applicationprotocol, so it directs it to HTTP proxy 2031. That proxy accepts themessage, then sends information it can obtain about the message'soriginator (access filter 403(3) from outer IP header 2203 and SKIPheader 2205 to evaluator 2036 to determine whether the session beinginstigated by this message should be allowed to proceed. Evaluator 2036examines the source IP address of the message as well as the otheridentity information, and by looking up the source IP address in the MMFfile DBServerIDByIPFile, determines the identifier in data base 301 foraccess filter 403(3), uses that identifier to locate access filter403(3)'s certificate, and finds that certificate information matches theretrieved certificate associated with access filter 403(3)'s messagebeing processed. The source of the message, access filter 403(3), isthereby recognized as an access filter 403 within VPN 201, so evaluator2036 responds that the session should be allowed, for the reason that itis a message already permitted by another access filter 403 within thesame VPN 201. This decision to allow the message is returned to the httpproxy 2031. The evaluator 2036 will instruct http proxy 2031 on accessfilter 403(5) to allow any request that comes over the same session, forthe same reason. As the http request is processed, the proxy willestablish an outgoing connection to the http service on server 407, inthe same manner as the outgoing session was established on access filter403(3).

When the connection is initiated to server 407, evaluator 2036 looks upthe IP address of server 407 in the MMF file DBServerIDByIPFile todetermine the identifier in database 301 for server 407, uses theidentifier to locate the table for the server, and uses the certificateidentifier from that table and the DBCertificatesFile to find thecertificate for server 407. Then it uses the keys for access filter403(3) and the public key for server 407 (obtained from the certificate)to construct a SKIP session as described previously. The actual messageis encrypted and authenticated, a SKIP header 2205 is added, and anouter IP header 2203 is added, directing the message to server 407.

When the message reaches server 407, SKIP in server 407 checks theauthentication on the message, decrypts it, and forwards the decryptedmessage to the HTTP service, which performs the access to the Web pagerequested by the message contained in the payload. Having obtained theWeb page, the HTTP service makes a return message with an IP headerspecifying roamer 503 as the destination. This return message is thenencapsulated in a SKIP message 2201 as previously described. This SKIPmessage is directed to access filter 403(5) and contains the informationin outer header 2203 and SKIP header 2205 that is required for a messagebetween those entities.

When the reply message reaches access filter 403(5), it is authenticatedand decrypted by SKIP 2021 there, and forwarded to IP filter 2019. Themessage is found to match an existing session so evaluation is notneeded; it is forwarded directly to HTTP proxy 2031. There it is checkedfor validity as an HTTP protocol reply message and retransmitted back tothe originator of the HTTP session, which is access filter 403(3).Checking by the anti-virus module 2033 is not done since the originatorof this session is known to be another access filter 403 in the VPN 201,as it is known that access filter will do the checking if needed. Theretransmission of the reply is again processed through SKIP 2021 andencrypted as above, using the SKIP parameters required for an exchangebetween access filter 403(3) and access filter 403(5).

When this reply message reaches access filter 403(3), precisely the samething occurs, that is, the message passes through SKIP 2021 and IPFilter 2019, to the http proxy 2031. There it is checked for validity asan HTTP protocol reply message, possibly passed through the anti-virusmodule 2033 (if the message content type warrants it), and retransmittedback to the originator of the HTTP session, which is roamer 503. Thetransmission of the reply is again processed through SKIP 2021 andencrypted as above, using SKIP parameters as set forth above for amessage being sent from access filter 403(3) to roamer 503. The replymessage is then received at roamer 503, where it is authenticated anddecrypted by SKIP, provided to the user's browser, and displayed for theuser.

Conclusion

The foregoing Detailed Description has disclosed to those skilled in thearts to which the Detailed Description pertains the best mode presentlyknown to the developers of the access filters disclosed herein ofconstructing and using access filters that overcome the scalabilityproblems which prior-art prior-art access filters presented for virtualprivate networks. The scalability problems are overcome by a number offeatures of the access filter disclosed herein. Among them is an accesscontrol database which permits delegation of administrative authorityand administration of a local copy of the access control database andthereby allows decentralization both with regard to administrativepersonnel and with regard to geographic location. The access controldata base specifies access policies that determine which user groups mayaccess which information sets, policy maker policies that determinewhich user groups may make access policies, and administrative policieswhich determine which user groups may administer objects in the virtualprivate network. It is these administrative policies which permit easydelegation.

Administrators can employ the graphical user interfaces disclosed hereinto administer the access control data base. The clarity and ease of useof these graphical user interfaces makes it easy to delegateadministrative authority to non-specialists. When an administrator makesa change in the access control data base, the change is first made inthe local copy of the data base for a given access filter and thenpropagated to the local copies of the other access filters. The localcopy of the access control database also makes it possible toefficiently implement a graphical user interface to the virtual privatenetwork which shows a user only those resources that belong informationsets to which the user groups to which the user belongs have access.

Another feature of the access filter which contributes to scalability isthe ability of the access filters in a virtual private network toauthenticate sessions to each other. Because the access filters can dothis, access checking of a request need only be done once, at the firstaccess filter encountered by the request. The other access filtersbetween the user and the information item need only determine whetherthe request has already been authenticated by another access filter, andif it has, pass the request through. Authentication of sessions by theaccess filters to each other thus both decreases the amount of accesschecking that need be performed and distributes the access checking thatis done throughout the virtual private network.

Authentication also permits encryption to be done in the same fashion:the first access filter encountered by the request encrypts the requestafter it has checked the access, and the other access filters pass theencrypted request through without decrypting it until the last accessfilter before the server that contains the data item being accessed bythe request is reached. Doing encryption and decryption in this fashionreduces the amount of encryption and decryption and distributes theencryption and decryption that is done in the same fashion as withaccess checking.

Another feature is that the access filter assigns a sensitivity level toan information set and a trust level to a mode of identification of auser making a request and permits the access only if the trust level isat least as great as the sensitivity level. In the preferred embodiment,identification by Internet address is assigned a low trust level andidentification by cryptographic authentication with an X.509 certificateis assigned a high trust level. If the identification used by the userin making the request does not have a trust level sufficient for thesensitivity level, the access filter can interactively request that theuser provide identification with a higher trust level.

The access filter also assigns trust levels to segments of the actualnetworks in virtual private network 201 and to encryption algorithms.The access filter analyzes the trust levels of the network segmentsbetween the user and the server that contains the information item, andany of them is lower than the information item's sensitivity, the accessfilter requires that the session be encrypted with an encryptionalgorithm whose trust level is at least as high as the informationitem's sensitivity level. If a segment between the user and the firstaccess filter or a segment between the last access filter and the serverdoes not have the requisite trust level, the first access filterrequires that the user or server encrypt the session with an encryptionalgorithm that has the requisite trust value before it will allowaccess; if a subsetment of the segment between the first access filterand the last access filter, the first access filter itself encrypts thesession using an encryption algorithm that has the requisite trustlevel. By requiring only the trust level necessary for an informationitem's sensitivity, the access filter reduces the burden of accesschecking to what is actually required for the information item; bypermitting the user to offer a more trustworthy identification and usingencryption to upgrade the trustworthiness of a segment of the network,the access filter provides flexibility without compromising security. Itshould be noted that in other embodiments, the first access filter mayencrypt the session as required for the server, providing of course thatthe encryption for the server is sufficient for the trust level of theresource.

While the Detailed Description has disclosed the best mode presentlyknown to the developers of implementing the above features, it will beimmediately apparent to those skilled in the arts relating to accessfilters that any number of other implementations which embody theprinciples embodied in the access filter disclosed herein are possible.For example, as pointed out in the Detailed Description, an accessfilter with the above features may be implemented as an applicationrunning under an operating system, as a component of an operatingsystem, and/or as a component of a router. Since an unlimited number ofother embodiments of the principles disclosed herein are possible, theDetailed Description is to be regarded as being in all respectsexemplary and not restrictive and the breadth of the invention disclosedherein is to be determined not from the Detailed Description, but ratherfrom the claims as interpreted with the full breadth permitted by thepatent laws.

What is claimed is:
 1. An access filter that administers objectsincluding a plurality of information resources and controls access by auser to an information resource of the plurality, the access filtercomprising: access control information including at least one objectthat specifies an explicitly-defined set of users, at least one objectthat specifies an explicitly-defined set of information resources, atleast one object that specifies an explicitly-defined access policy, theaccess policy defining access by a defined set of users to a defined setof information resources, and at least one object that specifies anexplicitly-defined administrative policy the administrative policydefining administrative access by a defined set of users to an object;and an access checker that responds to a request by a user to access aresource or to administer an object by determining from the accesscontrol information whether the requesting user may access the requestedresource or administer the requested object, the access checker beingone of a plurality thereof in a network, having a local copy of theaccess control information, and employing the local copy to checkaccess.
 2. The access filter set forth in claim 1 wherein: the accesscontrol information further includes user identification information;and the access checker employs the user identification information toauthenticate the user before determining whether the access policypermits access.
 3. The access filter set forth in claim 1 wherein: theuser employs a client to request access to the information resource; theclient includes a browser which display; a list information resourcesaccessible to the user according to the access policy; and the accesschecker uses the access control information to determine whichinformation resources are on the list for the browser.
 4. The accessfilter set forth in claim 1 wherein: the request may be a request tomodify the object.
 5. The access filter set forth in claim 1 wherein:the request may be a request to modify a relationship between the objectand another object.
 6. The access filter set forth in claim 1 wherein:the request may be a request to modify the administrative policy for theobject.
 7. The access filter set forth in any of claims 1 through 6wherein: the object is an access policy.
 8. The access filter set forthin any of claims 1 through 6 wherein: the object that specifies the setof users specifies the set as a subset of another set of users; and theobject that specifies the set of information resources specifies the setas a subset of another set of information resources.
 9. The accessfilter set forth in any of claims 1 through 6 wherein: the administeredobject specifies a user subset.
 10. The access filter set forth in anyof claims 1 through 6 wherein: the administered object specifies a setof information resources.
 11. The access filter set forth in claim 10wherein: an information resource has a sensitivity level associatedtherewith in the access policy information. the request to access aninformation resource has a trust level associated therewith, and theaccess checker permits access only if the trust level associated withthe request to access the information resource is at least as high asthe sensitivity level of the information resource; and the request maybe a request to assign a sensitivity level to an information resourcebelonging to the information subset.
 12. The access filter set forth inclaim 11 wherein: a user has a mode of identification associatedtherewith in the access control information; the trust level of therequest to access the information resource is determined at least inpart by a level of the mode of identification, and the request may be arequest to assign a trust level to a mode of identification.
 13. Theaccess filter set forth in claim 11 wherein: the trust level of therequest to access the information resource is determined at least inpart by a trust level of a portion of a path in a network between theuser and a server in the network which provides the informationresource; and the request may be a request to assign a trust level tothe portion.
 14. The access filter set forth in claim 11 wherein: thetrust level of the request to access the information resource isdetermined at least in part by a trust level of an encryption methodused to encrypt the request; and the request may be a request to assigna trust level to an encryption method.
 15. The access filter set forthin any one of claims 1 through 6 wherein: the objects are availableresources in a virtual network.
 16. The access filter set forth in anyone of claims 1 through 6 wherein: the objects are organizedhierarchically; and an access policy for a given object applies toobjects that are below the given object in the hierarchy to which theobject belongs.
 17. The access filter set forth in any one of claims 1through 6 wherein: each access filter further comprises: a policy editorwhich a member of an administrative user subset may use to make amodification of the local copy as permitted by the access controlinformation; and a distributor for providing the modification to theother access filters of the plurality.
 18. The access filter set forthin claim 17, wherein: another of the access filters maintains a mastercopy of the access control information; and the distributor provides themodification to the other access filter, receives a master copy with themodification from the other access filter, and makes the master copy thelocal copy.
 19. The access filter set forth in any one of claims 1through 6 wherein: the access filter is implemented as an applicationprogram executing under an operating system.
 20. The access filter setforth in any one of claims 1 through 6 wherein: the access filter isimplemented as a component of an operating system.
 21. The access filterset forth in any one of claims 1 through 6 wherein: the access filter isimplemented as a component of a router in a network.
 22. A data storagedevice for use in a system including a processor, the data storagedevice being characterized in that: the data storage device contain codewhich, when executed in the processor, implements the access filter setforth in any one of claims 1 through
 6. 23. An access control systemthat controls access by users to information resources, the accesscontrol system comprising: access control information including at leastone object that specifies an explictly-defined set of users as a subsetof another set of users and at least one object that specifies anexplicitly-defined set of information resources as a subset of anotherset of information resources, the sets of users and the sets ofinformation resources being organized hierarchically according to theirsubset relations; and at least one object that specifies anexplicitly-defined access policy, the access policy defining access by adefined set of users to a defined set of information resources, anaccess policy for a given user subset and a given information resourcesubset applying to user sets that are below the given user set in thegiven user set's hierarchy and to information resource subsets that arebelow the given information resource set in the given informationresource set's hierarchy; and an access checker which responds to arequest by a user for access to the information resource by determiningfrom the access control information whether the requesting user mayaccess the requested information resource.
 24. The access control systemset forth in claim 23 wherein: the access control system furthercontrols administrative access to objects and the objects in the accesscontrol information further include at least one object that specifiesan explicitly-defined administrative policy, the administrative policydefining access by a defined set of users to a defined object; and theaccess checker responds to a request by a user to administer an objectby determining from the access control information whether therequesting user may administer the requested object.
 25. The accesscontrol system set forth in claim 24 wherein: the request may be arequest to modify the object.
 26. The access control system set forth inclaim 24 wherein: the request may be a request to modify a relationshipbetween the object and another object.
 27. The access control system setforth in claim 24 wherein: the request may be a request to modify theadministrative policy for the object.
 28. The access control system setforth in any one of claim 23 or 24 through 27 wherein: the accesscontrol system is implemented as an application program executing underan operating system.
 29. The access control system set forth in any oneof claim 23 or 24 through 27 wherein: the access control system isimplemented as a component of an operating system.
 30. The accesscontrol system set forth in any one of claim 23 or 24 through 27wherein: the access control system is implemented as a component of arouter in a network.
 31. The access control system set forth in any ofclaims 24 through 27 wherein: the administered object is a user subset.32. The access control system set forth in any of claims 24 through 27wherein: the administered object is an information resource subset. 33.The access control system set forth in any one of claims 24 through 27wherein: the administered objects are available resources in a network.34. The access control system set forth in any one of claims 24 through27 wherein: an administrative policy for a given object applies toobjects that are below the given object in the hierarchy to which theobject belongs, whereby only an administrative policy that differs froman inherited administrative policy need be defined for a given usersubset and a given object.
 35. The access control system set forth inany one of claims 24 through 27 wherein: the administered object definesan access policy.
 36. The access control system set forth in claim 23wherein the access checker further comprises: an information resourceinformation provider for a browser employed by the user to view a listof set of information resources accessible to the user, the informationresource information provider using the access control information toprovide information about which of the sets of information resources areaccessible to the user to the browser.
 37. A data storage device for usein a system including a processor, the data storage device beingcharacterized in that: the data storage device contains code which, whenexecuted in the processor, implements the access control system setforth in any one of claim 23 or 24 through
 27. 38. An administrativeaccess control system that controls administration of objects byadministrative users, the system comprising: access control informationincluding at least one object that specifies an explictly-defined set ofusers and at least another object, the objects being hierarchicallyorganized, and at least a further object that specifies anexplicitly-defined administrative policy defining access by a definedset of users to the other object, the administrative policy for a givenobject applying to objects that are below the given object in thehierarchy to which the object belongs; and an access checker thatresponds to a request by the user for administrative access to the otherobject by determining from the access control information whether therequesting user may have administrative access to the requested object.39. The administrative access control system set forth in claim 38wherein: the request may be a request to make administrative policy forthe requested object.
 40. The administrative access control system setforth in claim 38 wherein: the request may be a request to modify therequested object.
 41. The administrative access control system set forthin claim 38 wherein: the request may be a request to modify arelationship between the requested object and another object.
 42. Theadministrative access control system set forth in any of claims 38through 41 wherein: the requested object specifies a user set.
 43. Theadministrative access control system set forth in any of claims 38through 41 wherein: the requested object specifies a set of informationresources.
 44. The administrative access control system set forth in anyone of claims 38 through 41 wherein: the other object specifies anavailable resource in a network.
 45. The administrative access controlsystem set forth in any one of claims 38 through 40 wherein: theadministrative access control system is implemented as an applicationprogram executing under an operating system.
 46. The administrativeaccess control system set forth in any one of claims 38 through 40wherein: the administrative access control system is implemented as acomponent of an operating system.
 47. The administrative access controlsystem set forth in any one of claims 41 through 40 wherein: theadministrative access control system is implemented as a component of arouter in a network.
 48. A data storage device for use in a systemincluding a processor, the data storage device being characterized inthat: the data storage device contains code which, when executed in theprocessor, implements the administrative access control system set forthin any one of claims 38 through 39.